You can easily build a robot that you feed sheet music, and that robot will then be able to press the right buttons on a piano keyboard.
This is not possible for a guitar (and others) because there is no unique mapping between the note on the sheet and the position on the instrument.
> Of course, on top of that, you also have a wide range of ways to modify how you play on a guitar.
Yeah, same with the piano. And I think, with most of all instruments.