Publishing a physical book is expensive, publishing a website is dirt cheap. For the publisher and author of a book it's much more imperative to release good content that people will want to read, cover to cover. You can find more extensive, in-depth, and up-to-date content on the Internet but where exactly and is the info all in one place? Websites are also often made with the assumption you'll jump around or that you know what you're looking for. If you're learning something new it's often best to have a linear, paved path and not be your own guide.

Edit: Someone else said it first but I was trying to say library books are "curated" in a roundabout way.

You can ask the receptionist “Where is the Linux section?”, walk up to it and there it is. And you can grab a book and skim through it to see whether it suits you.

You can also go to google, ask "How linux works" and skim through the results.

I'm not saying libraries are bad, they're obviously amazing (and yes, I've been to libraries lol). However, in these sort of questions OP is usually looking for personal recommendations, something that you already read, heard about or found interesting to share. Yes library has books, but which book would you personally recommend OP to read? Which one do you like the best and why?