Amazon is very big on no information sharing. This is why your Amazon confirmation emails don't indicate what you purchase (unlike any other online purchase anywhere) so that your email vendor (Google/Microsoft/Yahoo) cannot read what you are buying for marketing purposes. While we may in general understand that transactions don't typically have enough detail shared with the Wallets (which seems to be the term being used these days), I don't know what that means in detail (including support for e-receipts and other features).
I could see Amazon wanting to exclude Apple and Google, but I can't see them offering Wallet support and leaving out some of the players. It is weird that physical card contactless works, but not the virtual wallets. That would seem to me to be active disablement not just not yet supported.
Yes, Amazon Pay is making a new, big push relative to their old history, but we've seen that it is too little, too late. And the Amazon/Venmo (but not PayPal) partnership is supposed to be coming online soon too.