Another member already mentioned in his answer (now deleted), that adding those pre-selection options is very easy compared to actually catering them. I will try to elaborate on why this makes it actually desirable to offer those options in pre-selection.

It's more intuitive

Imagine you're booking your ticket online and come to the point where you have to select your meal option. The options that are presented to you include vegan but not vegetarian, as that's not served on the flight. If this is the first time you're booking a flight, you might not know yet that there will be no specialised meals for vegetarians. In this case you might start wondering why there is no vegetarian option. Maybe it's missing? Maybe you should call the hotline and ask them why there is no vegetarian option?

If it comes to that they already wasted your time and brain power and if you actually call their hotline because of that, it will also waste the time of the person answering your call. This waste of time could easily be circumvented by just offering all options, so everyone finds their option immediately.

This problem could also be solved by putting a note next to the selection that explained why some options are missing, but this would probably not be as effective, as it is terribly hard to get a computer user to actually read notes.

You also mentioned in the comments that you usually have to declare you dietary needs by calling the airline. In this case it looks like this argument doesn't apply as the customer doesn't have to select the option theirself. However, the person answering the call still needs to make the selection and they will probably do it in a similar manner to what the customer would do when online booking.

People answering calls at companies are usually trained in some way, so the company could just train them to select vegan if someone says they're vegetarian. This would make the vegetarian options superfluous again, but you also have to consider the cost to train your employees about one more thing and while that probably doesn't add much to the overall training cost, it is probably still cheaper to skip this in training and just let the phone operators believe all the options actually matter.

I don't think this is the only motivation to offer these options, but from an IT perspective this definitely makes sense.

Another member already mentioned in his answer (now deleted), that adding those pre-selection options is very easy compared to actually catering them. I will try to elaborate on why this makes it actually desirable to offer those options in pre-selection.

It's more intuitive

Imagine you're booking your ticket online and come to the point where you have to select your meal option. The options that are presented to you include vegan but not vegetarian, as that's not served on the flight. If this is the first time you're booking a flight, you might not know yet that there will be no specialised meals for vegetarians. In this case you might start wondering why there is no vegetarian option. Maybe it's missing? Maybe you should call the hotline and ask them why there is no vegetarian option?

If it comes to that they already wasted your time and brain power and if you actually call their hotline because of that, it will also waste the time of the person answering your call. This waste of time could easily be circumvented by just offering all options, so everyone finds their option immediately.

This problem could also be solved by putting a note next to the selection that explained why some options are missing, but this would probably not be as effective, as it is terribly hard to get a computer user to actually read notes.

You also mentioned in the comments that you usually have to declare you dietary needs by calling the airline. In this case it might look like my argument doesn't apply since the customer doesn't have to select the option themself. However, the person answering the call still needs to make the selection and they will probably do it in a similar manner to what the customer would do when booking online.

People answering calls at companies are usually trained in some way, so the company could just train them to select vegan if someone says they're vegetarian. This would make the vegetarian options superfluous again, but you also have to consider the cost to train your employees about one more thing and while that probably doesn't add much to the overall training cost, it is probably still cheaper to skip this in training and just let the phone operators believe all the options actually matter.

I don't think this is the only motivation to offer these options, but from an IT perspective this definitely makes sense.

Johns-305 already mentioned in his answer, that adding those pre-selection options is very easy compared to actually catering them. I will try to elaborate on why this makes it actually desirable to offer those options in pre-selection.

It's more intuitive

Imagine you're booking your ticket online and come to the point where you have to select your meal option. The options that are presented to you include vegan but not vegetarian, as that's not served on the flight. If this is the first time you're booking a flight, you might not know yet that there will be no specialised meals for vegetarians. In this case you might start wondering why there is no vegetarian option. Maybe it's missing? Maybe you should call the hotline and ask them why there is no vegetarian option?

If it comes to that they already wasted your time and brain power and if you actually call their hotline because of that, it will also waste the time of the person answering your call. This waste of time could easily be circumvented by just offering all options, so everyone finds their option immediately.

This problem could also be solved by putting a note next to the selection that explained why some options are missing, but this would probably not be as effective, as it is terribly hard to get a computer user to actually read notes.

You also mentioned in the comments that you usually have to declare you dietary needs by calling the airline. In this case it looks like this argument doesn't apply as the customer doesn't have to select the option theirself. However, the person answering the call still needs to make the selection and they will probably do it in a similar manner to what the customer would do when online booking.

People answering calls at companies are usually trained in some way, so the company could just train them to select vegan if someone says they're vegetarian. This would make the vegetarian options superfluous again, but you also have to consider the cost to train your employees about one more thing and while that probably doesn't add much to the overall training cost, it is probably still cheaper to skip this in training and just let the phone operators believe all the options actually matter.

I don't think this is the only motivation to offer these options, but from an IT perspective this definitely makes sense.

Another member already mentioned in his answer (now deleted), that adding those pre-selection options is very easy compared to actually catering them. I will try to elaborate on why this makes it actually desirable to offer those options in pre-selection.

It's more intuitive

Imagine you're booking your ticket online and come to the point where you have to select your meal option. The options that are presented to you include vegan but not vegetarian, as that's not served on the flight. If this is the first time you're booking a flight, you might not know yet that there will be no specialised meals for vegetarians. In this case you might start wondering why there is no vegetarian option. Maybe it's missing? Maybe you should call the hotline and ask them why there is no vegetarian option?

If it comes to that they already wasted your time and brain power and if you actually call their hotline because of that, it will also waste the time of the person answering your call. This waste of time could easily be circumvented by just offering all options, so everyone finds their option immediately.

This problem could also be solved by putting a note next to the selection that explained why some options are missing, but this would probably not be as effective, as it is terribly hard to get a computer user to actually read notes.

You also mentioned in the comments that you usually have to declare you dietary needs by calling the airline. In this case it looks like this argument doesn't apply as the customer doesn't have to select the option theirself. However, the person answering the call still needs to make the selection and they will probably do it in a similar manner to what the customer would do when online booking.

People answering calls at companies are usually trained in some way, so the company could just train them to select vegan if someone says they're vegetarian. This would make the vegetarian options superfluous again, but you also have to consider the cost to train your employees about one more thing and while that probably doesn't add much to the overall training cost, it is probably still cheaper to skip this in training and just let the phone operators believe all the options actually matter.

I don't think this is the only motivation to offer these options, but from an IT perspective this definitely makes sense.