By not providing 3rd parties access to email, Apple makes themselves not only the controllers of the physical devices and also over the full identity of their users
Third party apps don't have to use e-mail for logins. They can use user names.
Backers of e-mail based sign-in often call it a "frictionless" method for the users to sign up. What it really is, is a frictionless method for them to collect information about their users.
As a user, I'd much rather use my email than have to make up a new username for every site. Emails are already public, it's not always some cynical conspiracy.
Uh, email addresses aren't already public - there isn't some magic email directory in the cloud (I mean aside from those aggressively hoarded by trackers, advertisers, and marketers because you had no choice but to use your real address once).
But this is also specific to "social" logins - eg ones where you aren't intentionally providing your email address.
They're a public endpoint designed to intake communications from anybody. Identity is an outcome from people using the same email, and that's a valid reason for using a proxy, but the address itself has always been public.
If you just have a username and password, what do you do for account recovery after a forgotten password? If not an email address, would a cell phone number be any better?
For accounts that really matter (not throwaways), someone needs to know a fair bit about the user's identity to ensure recovery works. It can be delegated (and probably should be), but that moves the identity problem rather than eliminating it.
Maybe someday we'll all have two Yubikeys (one for backup) and register with each website using them, but that's not how things work today for most users.
Google lets you set a backup email for account recovery.
I lost my original Reddit account because I never gave them my email address and it was hacked. (Using a throwaway password set back when I didn't care about Reddit.) I contacted support and they shut it down, but without some other way of knowing it belonged to me, wouldn't give me my account back.
Third party apps don't have to use e-mail for logins. They can use user names.
Backers of e-mail based sign-in often call it a "frictionless" method for the users to sign up. What it really is, is a frictionless method for them to collect information about their users.