Long-form writing definitely has its place in the learning process. Books can be a way to explain complicated concepts that require more background and detail than a blog post. If they're in dead-tree form it's easier to page to specific sections. And if they're in digital form then they're easily searchable.

Yes, experience matters, and I would absolutely recommend that anyone who wants to learn anything related to programming do lots of programming. But a book can be a good way to prime the pump and give yourself things to think about and mull over that will then impact your coding later. It changes how you view something.

Blog posts, videos, and such also have their place. We have a wealth of options available for different people with different learning styles, and that's a good thing!

In short, the answer to:

Why books?

Is because

Everything's online and better

is wrong. :-)

And while you may not "believe some people still buy books to learn", millions of people do. It's still a robust industry. (I've both bought and written tech books myself, although more the former.)