Guess what, people in college don't know either what textbooks you should buy. Maybe they're the teacher's favorite textbook, or a textbook the teacher wrote him/herself. Will that be the best textbook for you? Maybe. Maybe not.
Regardless, as mentioned before, if you think colleges do choose the best textbooks, you can find what textbooks they're using very easily.
My experience is that the best thing you can do is sample many textbooks and keep the ones you like best and are most likely to learn from.
That few people are willing to self-motivate for 4 years doesn't invalidate the possibility of doing it. I would also question the necessity to study for 4 years to learn most subjects.
The point about staying in your dorm is that if you're studying (i.e. not going out with your friends), it doesn't matter whether you're doing it at home or in a college dorm. You can socialize in other ways.
Serendipitous learning happens outside of colleges too. Etc. Etc.
Having been through college, and having learned a lot of things on my own, the only thing I think (some) colleges provide is just sheepskin prestige. If you want to work for a company that screens based on what university you went to, don't make the mistake of skipping that part. Learning-wise? I don't think it makes much of a difference.