College seminars are taken by people who want to be there.
If we're talking about K-12 education, that is for everyone and it's in society's interest that the most people learn the fundamental knowledge that we are trying to teach them.
I'm certainly open to the idea that our current approach is not optimal but I'd need to see evidence that a seminar-style approach would work in that setting. Maybe for some high school subjects. In fact some English classes were that way. We'd get a reading assignment, and then discuss in class, and then typically also have to write something about it on our own.
But math, sciences, and English topics such as grammar were all taught by lecture and example and I'm not sure the seminar approach would work as well there.