Do books sometimes say things that are obvious? Yes. For example, when I first read Martin Fowler's book Refactoring, I had been renaming variables and moving methods from one class to another for years. But he gave a new framework for thinking about something that obvious. I've found the idea of separating out my coding flow between adding functionality and improving code really helpful.
Can you get the material for free? Almost always, yes. But it takes time to find the right material, and our time is valuable. A typical industry book is $40-$50, and a typical text book is $100-$150. The authors of these books have spent time organizing the material in a helpful way that you would otherwise need to spend.
For some topics though, it's not just a matter of time savings. I'm working on a topic now that doesn't really have many useful books, so I'm having to read technical specifications produced by industry groups, which lack context and are pretty opaque. I'm missing having a book that explains these ideas in a coherent fashion.
I have tried a few MOOCs for professional development. I've found they can be helpful for a superficial understanding, but they don't encourage the deep understanding I get from reading through a book.