I totally interpret this as a move to prevent any sideloading and ensure data collection and ad injection are being done on their part. Can't easily prevent those on something that's not a fully baked Android.
Amazon doesn't have much to lose from allowing you to install x piracy app, in fact it's a selling point for a lot of people. yes a few people might not subscribe to prime, but I would be surprised if that outweighs the ad revenue and device sales
Run away from FAAMG, they all decided to behave like Apple.