[Quoth]

It's also expensive unless a whole series.

We are going to sell stuff on physical microSD cards. But that adds cost of card, time to reformat, copy, check it, post office time and cost of postage.

Then refunds are also more complicated.

Really the issue is the historic divving up the world, mostly between US based and UK based publishers and historically (up till 1960s) the USA often ignoring copyright of Non-USA content providers. Also related is differences in Libraries (UK & Ireland pay a per loan royalty) and for Music, the Performing Rights, which results in USA Radio stations paying less in royalty than European ones.

Many USA only titles, inc magazines had to be separately imported by UK & Ireland retailers as the wholesalers wouldn't stock them.

Publisher rights have historically been a mess. Geographically, translations, audio, ebooks, serialisations, animations, cinema, TV, plays and radio plays.
Amazon's solution is to be the only retail, wholesale and publisher.

Consult an expert lawyer regarding Agent and Publisher deals if you are an Author.

Some authors in UK and USA are objecting to the Housing of Random Penguins taking over Simon & Schuster. They claim it will result in less diverse publishing. I don't know about that, but certainly it might be good for consumers and Amazon is the Elephant in the Room that the authors are ignoring.