Chaosmancer
Legend
Yep. And guess what? There is nowhere near enough different stuff to warrant spending 2 years designing, developing, writing, drawing, cartographying, editing, and printing a new 256 page campaign setting "tome" for each of the other settings. I know you don't want to believe that-- or perhaps you believe they should be made anyway because you don't want to have to be bothered with doing it yourself... but it ain't happening. Not for 5E. Complain all you want about it, but it is what it is. Sorry, end of story.
But is there enough stuff to warrant putting 5 or more worlds into one book?
I think we could justify that, and it would be really helpful to new players to have a book hit the shelves that basically said " Those other settings you keep hearing about but have no idea what they are, here's a quick overview of each of them and a few of the special rules you might need."
I would have a hard time buying a single setting tome, I don't use anything except my own homebrew world, but a book like that I would snap up