Maybe it does happen. In fact, it certainly does. But you can't put everyone from a broad group into a limited box. One of the things you have to realize is that public schools, (and yes, I did attend a public school district,) tend to average out educational requirements. That means that slower students get left behind and quicker students are dragged down by everyone else, get bored and sometimes never reach their full potential. So you know those people who are obsessed with success? Some of those people pull their kids and use homeschooling to maximize their kids' potential and actually create an education that fits.
Other motives aside, one of the things you have to realize is that indoctrination seldom works. Children grow up. They get rebellious. A totalitarian mode of force-feeding viewpoints without providing a basis for why they should be believed is a wonderful way to put those viewpoints in a pretty shaky position, future-wise.