As many of us know, a MIDI sequence, no matter how accurate, cannot be easily transformed into a playable score. Enharmonic notes are not accounted for and rhythmic ambiguities will undoubtedly occur. There is also the problem of multiple voices. This is not so much a problem when the voices are separated in different tracks but is a major obstacle when they occur together on one track. Creating a playable score from a MIDI file would take more time than it would be worth.
Sheet music is relatively inexpensive.
There are also many Dover publications which offer high quality scores at unbelievable low prices. I own about 20 Dover scores myself and hundreds of dollars worth of scores by other publishing companies. I have received many compliments on my MIDI files and they are often featured at other sites as background music or offered for download. Every once in a while, somebody asks me why I do not add additional dynamics and customize my files to reflect the style of a 'human' performance. There are many reasons for this.