Dynamics aren't in the source material.

There's plenty of dynamic markings in music composed after the advent of the piano.

It would be in more modern music, but not Bach. Dynamics in music notation didn't come until the Renaissance.

Ah, I thought for Bach it was fair enough but Mozart is a different matter.

There is a huge difference between generating a series of notes, and generating actual audio. There can be dynamics in both. Just focusing on the actual notation is a much simpler problem. Trying to generate audio, requires not just notes, but tone harmonics, stochastic noise, rhythym, all sorts of properties that ears are extremely sensitive to.

No, the dynamics can be generated just like the notes. Actual scores have markings for dynamics and midi provides 1-127 dynamic points.

The dynamics are an important part of the music and can't be ignored