How does my three years of reading get compressed to two years? As I said, most recommend each hour of lecture time to be followed by three hours of self-study

How does my three years of reading get compressed to two years? As I said, most recommend each hour of lecture time to be followed by three hours of self-study. Also, if someone is going to do those three years of non-class study (after class in my case) so they can have my equivalent non-class study - why not just do the extra year of in-class work and get the diploma? The attitude perplexes me - "I will study three years like you, but won't get a diploma that will help in employment". No one is forcing me to go to class. But if I am taking a class on theory of computation, with quizzes etc., then it makes sense that that will be the months in which I read about pushdown automata outside of class. So after I choose which class to take in a semester, I am in a sense "forced" to study that topic outside class for the next four months. I can also e-mail my professor or classmates or wait after class or go to office hours if something confuses me.