Obviously, the more information we have about you, the easier it is for you to prove your identity! Often the people who lose all their credentials and can't get the account back at all are the ones who used anonymous payment methods, clear all their cookies, use a fake name. Hard to identify those!
But generally, we help people regain access with a combination of payment method, backup communication methods they have registered with us like another email address or a phone number, and at the most extreme - Government ID. Provide enough of those and survive the lockout period in which we've informed the person with access to the account and given them a chance to object, we can get you back in.
Seriously the "24 hour lockout while we make sure nobody is accessing the account" is a pretty key part of slowing down attacks - generally if someone's identity is stolen then the attacker's main advantage is speed rushing through all their other accounts, so the slow-down is hugely advantageous.