Your question phrases it as though it's a disciplinary practice to self-teach but in all honesty I just think it's a learning style and this happens to be my learning style. I've always been someone who learns best taking material given to me and going into a corner to understand it by myself. What makes me an excellent teacher to others is what makes me a terrible student to any other teacher in my life because I saw their participation and lectures obstructive more than enlightening.

What frustrates me a lot with being taught by other people is in my experience 90% of teachers have nothing to add that isn't already given in the course material, are too egoistic and impose personal biases, or just aren't curious enough to actually understand what it is that they're teaching enough to answer questions I do have. My history with dealing with teachers has always been "tell me your sources so I can study from those and make you irrelevant"

I've always been a person where if you give me the basics of 101 I make a point of ignoring anything anyone else has to say about it and work on identifying and classifying the patterns myself, because I want to understand the mechanisms behind whatever it is I'm learning so deeply that I can start fucking around and being inventive with it. You can't invent with repeating just what's told to you works.