The check on this is that you are now putting an inconvenience on that apps users. Maybe it’s okay in some isolated circumstance however, I imagine this won’t sit well if it becomes a reoccurring theme for iOS users, as they will come to view Sign In With Apple as unstable/unsafe (like Google and it’s graveyard). It would quickly render Sign In With Apple useless if the trust that it will continue to work whenever used is not there

I actually think this wouldn’t really happen in practice as consumers are quick to respond negatively to this behavior, so I’d be shocked if Apple actually did this without some darn good reason (I imagine it will also include removing said app)

Apple operates on behalf of the user. Apple saw users with throwaway/burner email addresses and said why not make this easier for everyone?

No more so than Gmail/Yahoo Mail/etc is for the average end user

Congratulations, now all of your email goes to a single different email address; your tracking profile is now associated with randomstring@email instead of john.doe@email.

If you wanted something truly private you could create an account at a provider like Fastmail or ProtonMail and create an alias for each account (or just wildcard a custom domain until you need to send from an address). I doubt any tracking system is based on the domain in your email address... not yet, at least.