Here my reason for not doing it (I usually teach rather elementary courses).

It will result in a large set of edited notes I have no control on. This means that some of those edited notes may well contain errors or do not reflect the spirit of my course and at the same time be very popular between students for being "condensed", "easy to read", "good to pass the exam". This will damage some students, that can get something wrong from the course because of sloppiness.

Also, as a personal experience, at least on one occasion I had someone trying to get some money out of my notes. Starting from the source file it would be even easier for them to rearrange the file in a form that makes it even harder to give them some trouble for this behaviour.

On the other hand we now have rather professional Pdf-Notes like softwares that allow everyone to underline, put on evidence, highlight whatever they want. With the positive point, though, that such modifications of the original file are clearly identified for what they are: additional material.