The fact that you know your password is what identifies you as the legitimate owner of your account. If you forget your password, you can't identify yourself as the legitimate owner of your account and thus, to the eyes of the system, you aren't. And about the only person who should be able to change the password of an account is its legitimate owner.

So, to answer your question:

Do they just ignore that rule in that case?

That case should not even happen in the first place.