Why write a book?

If you've never written a non-fiction book, there are a lot of reasons why you might want to. It organizes your thoughts. It's a big project worthy of your attention.

Noted.

But once you've written a book, it's not clear that it's a useful thing to publish one. After all, it takes a year. It involves a lot of people. You need to print a lot of copies, ship them everywhere, create a lot of hoopla and hope that people actually a) hear about it, b) decide it's worth the effort to track it down...