They sell more e-books because the publishing industry colluded to jack up the price of paperbacks so that $10 e-books look like a bargain. I'm not paying $15 for a physical book that would have been $5 15 years ago. Their production overhead has been dramatically lowered by digital distribution and I'm expected to pay more?

I think it's the convenience for both buyers and sellers. If readers want the book "now" they get the kindle version; if they want it later they get the physical copy. However, Kindle in general is a dark pattern: it forces users to be locked into their product ecosystem.