I was reading about Liszt, and I’ve heard it said about others, that the span of his/their hands were thought to contribute to his/their ability (although perhaps just with some works?). If this is true (is it?), why not just reduce the width of the keys a bit? Perhaps too many people are to used to the keyboard as is to “improve” it (ala the qwerty problem) or perhaps the keys are as narrow as can be managed, but if this could be done would an experienced player have more “success” with certain works? : )
Lots of cheap “kiddie” keyboards have reduced-size keys, so one could easily see if reduced key spacing has a real impact on playing. In the case of Listz, some of it might have been machismo; writing something that one’s peers/competitors couldn’t play like Scott Joplin did with “Tricky Fingers”. Same thing with Listz’ 93 note pianos.
Probably the same reason computer keyboards are built to a 3/4" width - any much smaller, and you’d be hitting two keys at once.
(Scoots off to measure the piano) The keys are 7/8" wide. So, they could be shrunk a little, perhaps. But not much.
Two things - the spacing between the black keys matters - if that gets too narrow, then your fingers bring down the surrounding black keys as well as the white key that you’re trying to play. You have to be able to play with your fingers along the edge of the black keys so you can play chords with a mix of black and white notes. I have wide enough fingertips that some pianos catch me out.
Also, you don’t carry your own piano with you unless you’re rock-star wealthy - you have to be able to play the same music on every piano you encounter, whether it’s a top-level 9 foot concert grand or a PSO (Piano Shaped Object). Standardization is enforced - if your keyboard is different, a top level pianist will notice.
There’s a story about Glenn Gould going to a Yamaha factory and playing a new piano they were working on. He played half-way through one of the Bach preludes and fugues and stopped, saying ‘The keyboard is too short.’ The guy showing GG around the factory told him it was the same size as every other keyboard. GG said ‘Prove it.’ They got a tape, measured, and found it was about 5 mm shorter than standard. Gould could tell, and so could anyone else who has put in his 10,000 hours learning the minute difference between the right chord and a clam…