The question is, why don't more people avail themselves of these (mostly) free resources? I think that the answer is that the majority of people don't care, and don't feel as enriched by knowledge for the sake of knowledge as the average hn member, or even the average college student. After a hard day of menial work most people want to relax and watch tv or have a beer with friends. The majority of people care about "education" in as much as it can help them to get easier and higher paying jobs, as far from laboring as a line cook as possible. Let's not pretend that the average McDonald's worker is thirsting for knowledge about the humanities or would materially benefit from it in any way.
The idea that everyone should be pursuing secondary education seems like a bit of projection. If general education classes were beneficial to you, then that's great. But most people are more concerned with their families and relationships, paying their bills and enjoying life in their own way than they are with learning and personal growth. If a trade school is the best way for them to do those things, then so be it. Telling people to study things they aren't interested in because "it's good for them" probably isn't going to help much.