Amazon didn’t have to. Netflix doesn’t. Apple is a lot more lenient about which apps can get on the AppleTV than Roku. Roku wants a cut of ad revenue and forces each provider to make special deals.
Amazon agreed to do it in in exchange for a lower revenue share with Apple. This is in the article. All I did was summarize what was said in the emails.
It was a mutual deal. Netflix chose not to. Other streaming providers choose not to have in app purchases at all and still integrate. Either way it’s the provider’s choice.