That's a terrible idea. Back when MSN was one of the most common instant messengers, there was a common prank that was called "freezing" where you just continuously kept trying to log into someones account and it would lock itself out for 15mins or more depending how long you kept doing it.

There was automated tools that did this too!

That's the first obvious countermeasure and will prevent hackers targeting a specific account. But there are other ways to crack passwords, one is to try the same password but iterate over user ids instead. As hackers would start with the most common password you can't throttle globally on same password attempts either because well yeah, it is by definition the most commonly used one which should have a lot of traffic.

"Credential stuffing" as I've heard it used refers to taking username/password combos from one breached site and trying them in other sites.

So for example LinkedIn has a breach, which reveals to evildoers that user 'johnsmith@example.com' uses the password 'smith1234' then they test that username and password in Amazon, Netflix, Steam and so on.

They only make one attempt per account, because they only have one leaked password per account. Hence, throttling per account isn't an option.

That would create an easy denial of service attack: if I wanted to deny you access to your account I'd spam it with bad login attempts.

With credential stuffing, isn't it unlikely the perpetrator wants to make more than one or two attempts per user ID?