Then they'd likely get sued because the license for the answers are CC-BY-SA, putting them in a book, claiming they wrote everything themselves, and selling them are all against the license.

On the other hand, if they read my answers and they wrote a book about what they learned (not copied). There'd be no issues

Well if the book was doing well, I might clone it and sell a few copies myself

Let's be real, SO is a troubleshooting site. It's not our personal collection of code or project sources.

I don't expect to be paid when someone asks me for directions, and I'm sure lonely planet didn't source their guides 100% organically either.

What if I read your answers, claimed I learned everything myself, and sold my skills to a company for money?

That would be a very different scenario. Learning isn’t copying, but that is.