You're looking at an exploit from a technological point of view, which I expect this community is likely to do. Think of it from the perspective of the average user. I know for a fact if my mom was told by an attacker "if you see an approval request for your account, just accept it" she would do so. It's taken time to train her not to give anyone her password.

I've read of attackers with valid passwords spamming logins in hopes to trick a user into approving the auth. Whether it's because it woke up the user and they're in a sleep fog, or they're busy and not paying attention.

Microsoft, at some point, changed their login flow so that, by default, when you enter your username, it sends a pin. I receive regular attempts at this. This isn't going to work out for the attacker because they have to get the pin. But if all that's required is a button press, the attacker could just make the login request and wait.

With multi-factor auth, where a password is in use, you have to get past the password before getting to that auth approval. It reduces how much noise the user gets and the chances of success for the attacker.