I think it's to protect against the Identity Provider revoking access to the service you're dealing with rather than them blocking your account.
We saw this recently with "Sign in with Apple" and Epic Games, where Apple denied access to Epic and the accounts that did not share their actual email were effectively lost.
> Apple previously stated they would terminate “Sign In with Apple” support for Epic Games accounts after September 11, 2020, but today provided an indefinite extension.
