We might as well question certain assumptions that have been around that long. A good way to start is refretting guitars. Standard guitars are fretted to 12 tones per octave, conforming exactly to the keyboard of the piano or organ. Because it's the simplest and cheapest way of tuning an instrument to fixed pitches that will produce any worthwhile music. They also use bottleneck sliders to get pitches between the frets.
Some synthesizers make provision for bending tones.
So the desire is there. Well, that depends. Now there are enough possibilities to go around. These can all be done on guitars by changing the frets, since I have compiled fretting tables. New electronic instruments can be tuned to them, and there are electronic tuning devices to make this possible for average persons.