Part of this is the complexity of the interface (I.e. Piano keyboard vs. violin, etc.) need to be matched by complexity in controllable modulation a in the synt

Part of this is the complexity of the interface (I.e. Piano keyboard vs. violin, etc.) need to be matched by complexity in controllable modulation a in the synthesis engine. The history of musical synthesis was a piling on of complexity up to about the late 90s then there was stagnation (or to a degree even reversion.). Part of this was simply the ability for users to reasonably build sounds with some of the more complex synth engines, but I think a lot of instruments (at the time they were mostly sample playback subtractive synthesis) couldn't build the complex nuance of sound from a natural system. In the mid 90s Yamaha came out with a synth called the VL1. It was hugely expensive and used physical modeling waveguide synthesis. It modeled a vibrating column of air in a wind instrument, and to program it you needed special software to design the construction and shape of the instrument (this was radical because all synthesis at the time was about controlling the sound.) It was actually possible to create instruments that couldn't play in tune, or wouldn't even make a sound. This instrument really responded well to complex inputs and was especially sought after by EWI wind players (the original was a keyboard instrument, but required a breath controller to play most sounds since the sounds were designed to require constant energy going into the system to make sound.). But it turned out to be exceptionally difficult to make musically useful sounds, and unlike most pro synths of the time, you couldn't program the models until some years later yamaha released their internal sound design software. Since then most commercial synths have either been multipurpose sample subtractive, or virtual analog that simulate the old analog synths from the 70s.