[Earw0rm]

That's because MIDI doesn't contain all the information that was in a score.

Scores are interpreted by musicians to create a performance, and MIDI is a capture of (some of) the data about that performance. Music engraving is full of implicit and explicit cultural rules, and getting it _right_ has parallels with handwritten kanji script in terms of both the importance of correctness to the reader, and the amount of traps for the unwary or uncultured.

All of which can be taken to mean "classical musicians are incredibly picky and anal about this stuff", or, "well-formed music notation conveys all sorts of useful contextual information beyond simply 'what note to play when'".

[pclmulqdq]

A lot of modern scores are written with MIDI in mind (whether or not the composer knows it - that's how they hear it the first 50 or so times). That should make it somewhat easier to go MIDI -> score for similar pieces. Current attempts I have seen still make a lot of stupid errors like making note durations too precise and spelling accidentals badly. There's probably still a lot of low-hanging fruit.

This is absolutely not easy, though, given all the cultural context. Things like picking up a "legato" or "cantabile" marking and choosing an accent vs a dagger or a marcato mark are going to be very difficult no matter what.