So can someone explain to me why the downvotes? If the salts are unique to the user wouldn't it be nearly impossible for the hacker to use the hashed pw on other sites? (I'm not a web dev but to my understanding that's how it works)
That's because the user specific salts were probably in the same db. This will make it difficult since a brute force attack must be done for every single password. But it is still not impossible.
Even if the salts aren't unique, can you explain how can they use the hashed password anywhere?
If I give you a hashed password and the salt used, what exactly can you do with it? (apart from brute forcing)
A password DB breach, salted or not, allows an offline, non-rate-limited, attack on those passwords.