If you're not gonna know as a junior in college, having been through high school, any better than you did as a 8th grader - why bother with it at all?

Because, as an 8th grader, I wanted "computers". Now, I although I still want "computers", I don't know if I want to focus on web/scripting languages, on embedded systems (or something in between), on computer graphics or on UI/UX, etc. Now, I know what fields I have available to pick from, and have (some) experience in most of them. I can make more of an informed choice now then I could have a decade ago. I can tell you that as an 8th grader, I wouldn't have been able to understand most of the things that I do today.

Maybe some people aren't exposed to enough options in middle school.
I think its because when you're 9-13 years old, theres limits to what you're capable of doing and what you know. Its completely and utterly impractical to even pretend that it is possible to expose someone to every field and topic by the time they're 13.

..fully 75% of the student's time is wasted learning facts and skills that are unimportant.
See, I don't (and didn't) think think that any of my classes were unimportant or useless. I might not have cared about them. But I could see the value in the fact that the knowledge is there and in knowing the basics of the topic.

I might not be an English major, but I can read a book and then be able to understand it and write about it in a coherent manner. The ability to write (and therefore express yourself) is very important to have. I might not do anything with Chemistry or Biology, but at least now I can look at a food label, read the list of ingredients and (somewhat) break down whats in the food, to figure out how unhealthy it is for me. I might never need to know about the causes of the Industrial Revolution or what the big deal about the Enlightenment was, but, in its own way, thats exploring human thoughts and behaviors - that still influence the world today.

I had to fill a "Modern History" requirement here at college. I took International Relations. I found it interesting enough so that I took on a second major to study it some more.

The knowledge might not be directly useful to you. But its knowledge. And you can take it, and with some thought, apply to the rest of your life. The concept of learning the basics about a number of fields wasn't randomly chosen by people hundreds of years ago for no reason. They were onto something. That something might not work well for everyone. I'm not going to pretend it does. But, a majority of the time, it does work.

Schooling and learning — all of it - is what you make of it. At the end of the day, if you choose to make nothing of it, thats your choice. If you think that you can learn more on your own, then I hope that you're right. Because learning is something good, you should enjoy it, not hope to get out of the way so you can make money.

Oh, just for laughs, I went back to my elementary (primary) school yearbook. In the "When I grow up, I want to be.." field, I had down: "Baseball Player, Stock Broker, Lawyer, Scientist". This completely changed after Middle School. If that yearbook asked a similar question, the answer would read "Computers, Musician, Author, Politician". By the time I graduated High School, it would have read "Computers, Journalist, Graphic Artist". In college, if I had to fill out that field, it would likely read "Computers, Something to do with international politics, Author"