Because the stupid schools - like the one I attended way back - teach about languages, not languages. I spent four years "studying" Russian
Why don`t you start reading the discussion from its beginning? The OP mentioned the modern language school while you are talking about regular high school from 1960s.
I hope that after some thinking you will understand these are two different things.
The native teacher helped you get rid of your psychological barriers in speaking Polish. The same thing may happen in a language school, if you trust and like the lecturer/teacher. Probably it won`t happen doing an online course.