why would anyone write a book for o'reily (or anyone) for such low royalties?
How much money is there in "Game Programming for Haskell", really? You release with O'Reilly and you get 10% or $1,000. You self-publish and you make more per sale, much more, but make much fewer sales - so, let's say $3,000.
But publishing with O'Reilly, you get accepted on the speaker's circuit and start getting asked to do contract work; publishing on your own, you don't (as much). It's arguably worth losing out on a one-time gain of $2,000 for that.
I'm not sure that attitude is deserved. There are pros and cons with going through a publisher and am very unlikely to do it again. (Reputational benefits are pretty irrelevant to me at this point.) But no one should go in thinking it's about the money.)
People author these books to increase the value of their personal “brand” or out of a passion for whatever technology they write about. If they are hoping to get rich or get a “livable” wage… they are going to be very disappointed.