Haha, that's the classic thing with platforms that have demand aggregation. They extract a lot of stuff. DTC, Telehealth, all these things end up paying Meta and Google a large fraction of their revenue. Same with Stripe et al. The idea is to take a rake on all spending. It puts you in an unfathomably strong position. It's why Visa and Mastercard are such good businesses.

To get something in front of someone you need to do some work. These guys have the people so they charge you to show it to them. I'm realistically not going off Amazon. If you want to list the ebook on your website maybe I'll buy it there, but if you do a physical copy your 'tax' is going to Shopify. That's how it is.