I think for Google and Apple this is more of an agreed upon API to replace the multiple "login with X" buttons. Instead of having "Login with Google", "Login with Apple", "Login with Facebook", and "Login with GitHub", there is just one login button that uses your ecosystem of choice. That's the part that should make the process simple for users. Less choice.

In other words, it's to help you easily login to everything else. But your main account would still be protected by a password. Otherwise you wouldn't be able to replace a lost device.