They can, and then they’ll have to face their customers directly with it being exactly clear (even to “normies” who don’t follow obscure tech news like this) exactly whose greedy fingers are taking things away from them.

Up till now, situations like Kindle were just weird quirks to most people and most people wouldn’t have been able to tell you why you can’t do this very normal-seeming thing on iOS. If/when Apple takes it away, it’ll be obvious to everyone what’s going on.

There are plenty of no longer supported apps on people's phones.

No one is blaming Apple for it.

I think it'd be a bit different if Kindle, Spotify, Netflix and co. all suddenly stopped working/got worse.

And if Apple yoinks them out, then why should the developer respect the "no disparagement" or "no telling your customers about payment/alternatives"? Which to me was always the ultimate expression of Apple absolutely knowing they are being greedy. Not just "You can't tell your customers you can pay less elsewhere", but "You can't even tell your customers about our involvement in your pricing decisions".