[jamesgeck0]

The difference is that Apple's sign in is beneficial for non-technically savvy users, as it both allows using an anonymous email alias and alleviates the need for password creation. Those are both reasonable privacy and security trade-offs for a tiny bit of (generally reversible) ecosystem lock-in.

[clusterfish]

Tiny bit? Try and migrate dozens of app accounts to a non-Apple email, as a non-technical user. Disregarding the sheer amount of work, such users won't even know how to send emails from the private addresses they signed up with, making it hard for app developers to identify them. It's always about control and lock-in with Apple.