[IAmPym]

When you take audio out of the equation you don't need a lot of things:

What makes the sound? Not needed anymore. So any ADC/DACs, DSP code, analog voice hardware, etc is not needed. The DSP in particular is fairly complex and can be expensive depending on what you're doing

If you take the analog side of things out you don't need as complex power and all sorts of other things, so you may not even need a power supply at all, which is huge! Etc, etc.

Then there are things in the middle, like CVs, which are 'kinda' audio but not really since they are just control voltages. You can run them quite slow and still be useful (like 10kHz even). Or, you can treat them like audio, which is definitely my preference, so it depends on your implementation.

MIDI is a great place to start on a path to developing your own instruments. The amount you can do with a controller is CRAZY when you start to see how far it can go