I struggle to comprehend how you can think they are not.
They are not. IP law is very clear on this.
If I write a book, should Amazon be able to take it and monetize it while paying me nothing for my original idea, just because they are a big corporation?
Your book isn't your idea. They are two different things. People can copy your idea; they can't copy your book.
Ideas are cheap and easy to come by. As I've said before, I can have 30 ideas while enjoying a few beers at the pub. Hell, I just had one while I was typing that sentence! The idea is easy; the hard bit is the
work, and that's what is protectable.
There are three common broad things which are protectable:*
1) Copyright -- the
actual words/art. You can write a fantasy book where elves and dwarves fight a dark lord; you can't copy and paste LotR.
2) Patents -- it's easy to have an
idea to make a time machine. To protect it you need to patent an actual design.
3) Trademarks -- logos and names which are used to convey to the customer who made the thing so they know what and from whom they are buying. You can write a fantasy adventure about heroes fighting dragons in a big war of dragons, but you can't call it
Dragonlance or put the D&D logo on it.
The thing that's not protectable--ideas.
*there are other things, like trade secrets and stuff, but that's really beyond the scope of this post.