The thing I feel I got the most out of in college was the structure. Sure, I could have self-taught myself, but it's difficult when you don't know where to start. One of my bachelor's degrees was in linguistics. I didn't already know what the different subfields are and what order I should study them in. And even if I did know that, I wouldn't know which works are considered the most important in each of those subfields. I've noticed that people who have self-taught the fields I studied in university often have gaping holes in their knowledge of things that are vitally important to the field. It isn't their fault since it can be hard to assess your own knowledge, but it's not a problem a university-educated person would have (unless they just slept through all their classes of course ;)).

And reading isn't everything; I tend to be someone who learns by doing. And doing linguistics (or anything else) is hard when you don't know where to start or have other people to do it with! Trying to do phonological derivations where you need to identify rules that lead to surface opacity is not something a beginner can do, but you wouldn't necessarily know that from self-studying. Instead, being given homeworks that gradually increase in complexity eventually prepares you for that. Plus, going to professors' office hours and talking through problems was always immensely helpful for me.

Beyond just learning your chosen field, being prepared for a career in that field is another thing that universities offer. Having gotten close to professors through classes, I could then work on research with them independently and (1) get valuable career advice from them and (2) get letters of recommendation from them.

So I guess I'd say that it's the guidance and structure you get from universities that is really valuable.