Given the many advantages of using a zero fret on a guitar (as cited in this excellent answer Advantages of a zero fret) and given that with a zero fret it is easier to play chords that call for strings to be fretted at the first fret (F Maj Barre) - why is it so very rare to see a guitar with a zero fret?
What are the disadvantages to the use of a zero fret?
Why is it that even among the most expensive guitars such as Martin, Taylor, or Gibson - a zero fret is quite rare?
To make it safe against buzz, the string has to run across the zero fret with a bit of pressure. This makes the strings move across the fret with some stickiness so they follow the tuning machine more hesitatingly. In effect, you get some of the downsides from most tremolo bars with regard to tuning stability.
In addition, frets get indentations from playing eventually even though the strings are mostly static with regard to non-zero frets. The zero fret, however, is still in contact with the strings while tuning so it gets more of a filing action and can develop creases which are in turn bad for string life.
So it's "your mileage may vary" terrain.
I installed a zero fret on my Fender a few months back. It smoothed out the tuning (no more 'jump' due to friction at the nut) and dropped the action at the nut to the perfect height. Perhaps it just runs counter to tradition?
EDIT: I bought a new Seagull Rustic Mini-Jumbo 2 days ago. The action was quite high, so I cut down the saddle and installed a zeroth fret yesterday. I saved the original nut and used an old nut with slightly wider string spacing. The action is now super low at the first fret.
This is just a guess, but perhaps not utilizing a zero fret is mostly habit/tradition as much as anything. Slightly earlier fretted instruments used gut string tied around the neck as frets which had to be replaced pretty often. A plain nut would be better all around in that case. Then metal and metal work was probably expensive as well. By the time all that changed luthiers and musicians were probably just set in their ways. High end guitars are still a lot like they were 150 years ago. Even the most popular electrics are designs from the middle of the last century.
the zero fret gets a ton of corrosion and wear starting right away - intonation would immediately start to fall off (a tiny discrepancy starting out) but in no way would it be as consistently static as a variable in tuning, tone or playability as a bone/metal/stone nut. I would also have concerns about lateral string movement which causes plinking noises as it slides over the imperfections of zero fret, that could ruin a recording easily, and worst case strings jumping out of their rut (it will happen). lastly, zero nuts would need replacement as a prerequisite to setting up your guitar's intonation correctly once it has some wear on it, it would throw off the action.
A zero fret overcomes the problems of poorly cut nuts and provides excellent intonation. It's cheaper for manufacturers to skip the zero fret so that's what they tend to do.
my 50s Hofner senator has a zero nut which has prompted me to fit them on all my guitars. Most "nut only" guitars the slots are not deep enough making fretting at "1" more difficult than it needs to be. Plus to my sorrow attempts to deepen the slots often end going too far.
If manufactures can level all the other frets they can do so with a zero fret for little (if any) extra cost, the nut should only space the strings not set the height.
It takes precision to place the nut at the correct location, however, say a guitar neck maker were to produce in many or mass quantities necks for a certain kind of guitar. That maker would not have to be concerned with the exact placement of the nut. The maker would simply add a fret at that correct location (negligible cost) then install a nut behind it. As guitar making came to be known as an art in modern times it became more of a professional stamp to remove the zero fret.
I have read many times that a zero fret for a guitar is a less expensive neck to manufacture.
I have only witnessed a zero fret on inexpensive guitars.
For whatever that is worth.
