There are math input methods that are on par with handwriting, e.g. texmacs or mathcad
Using a blackboard affords more time to actually taking notes. I could follow the derivations as they happened, and would frequently catch mistakes like a missing sign.
In addition, at least for me the act of writing them down engages different areas of my brain. I think more about what I'm writing when taking notes by hand, while typing LaTeX or similar on the fly causes me to think more about how.
For me, writing notes by hand from a teacher using a blackboard with prepared notes lead to orders of magnitude better recollection and understanding.
If all the teacher had was PowerPoint slides, I typically barely recalled anything.
Probably because you were in a coma.
Of course I did recall some things, but after a few semesters I found PowerPoint-oriented classes to be barely worth attending. This was in stark contrast to the blackboard-oriented classes, which I found immensely valuable.
The way you take notes during self-directed studying is important, and should be tested, but wasn't.
Was there a different study somewhere that wasn't focused on lectures?
Experiential salience is important for learning. It would be like copy and pasting code without typing it out yourself re a tutorial.