What is the purpose of a college degree? If I teach myself a subject from reading books about it, how is it any different from paying expensive tuition to learn the exact same information?

There's not just one answer and others may add their own. But your question equates getting an education with acquiring information, and that's not a good way to think of it. I'll use philosophy as an example, but some version of what I'm about to say would apply to any discipline I can think of.

A philosophy student may acquire a lot of information—for example, about who the Utilitarians were, and what compatibilism about free will is. But that's a small part of what she gets through her philosophical education. What she gets, if things works out, is the ability to think well philosophically. That comes from practice, from interacting with philosophers and, crucially, from getting feedback. It's hard to learn to do philosophy if all you have is a library of books that you read. In particular, it's hard to know whether you're learning to do it well. And—trust me on this—your own judgments about that may be way off the mark.

There are exceptions, of course, but they're just that: exceptions. You may be one, but your question itself suggests that you may not be. That's not meant as a put-down; very few people are exceptions in this way. I know I wasn't; I doubt that any of my colleagues were.

As I said, the point doesn't just go for philosophy. A great deal of what you learn when you study a discipline with people who've mastered it is tacit knowledge that can't be reduced to a collection of facts. A good deal of education is socialization. You learn how to think in the ways that people in the discipline think, do the kinds of things that they do. In every discipline I can think of, facts are in many ways the least of it.

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