I am currently DMing a campaign for a player that I will call Will and 2 others. To start off, Will is not really a problem player despite this question being tagged as such. He is engaged in the game, he does not cause problems for the others and the game has been going smoothly so far. I know Will has trouble keeping track of his sheet, his modifiers, etc, but since we started using the Avrae bot this has no longer been a problem.
However, Will is not good at creating characters with actual motivation. Will's character's just a simple native of the starting town who lives with his artisan parents. Most of his character "backstory" was trivia like favourite colour or random habits. The character is pretty much a self-insert, including the fact that he is pretty lazy and unambitious.
Will said that his character's initial reason would be to run some errands for his parents that were related to the "start of the campaign and initial quest" information I gave to everyone. Once that was done, I got his father kidnapped by some criminals. I am afraid that eventually, in order to keep Will's character involved, the campaign will end up feeling very Will-centric. The other players are much more flexible, meaning that their characters have more of a distant long-term goal and can be drawn by pretty much any plot hook or quest.
Some background: I've known Will for more than 2 years now and before playing DnD, we have been doing freeform RPs. All his characters were either political wish fulfilment (leader of his dream country) or meek, shy, lazy and unambitious characters. Will was the one who recently personally requested that I run a DnD game for him, and he refused a one-on-one, saying that he wanted to socialise. Will is aware that his character is not adventurer-like and does not want to be a My Guy problem player, hence why he added that his parents were making him run errands. However, Will does not know how to create a more adventurer-like character with long term goals. He simply has trouble roleplaying as a character too different from himself (generally, he doesn't know how to put himself in an imagined character's shoes).
Question: how can I help a player roleplay a character with long-term goals, as a series of short-term goals will eventually run out of steam and make the campaign feel this-player-centric ?