If an attacker already has access to your user's table (as is implied by most of the situations in this article), then they probably have your whole database. What else is there to lose? Why would an attacker bother to use any method to match passwords to hashes? Don't they already have everything they could want?
No, they do not. Maybe an important person's password hash gets leaked and they want to extract the password to check other sites for reuse to get into other systems. Now you say reuse is dumb, and I agree, yet a lot of people do it because they're lazy. This is just an additional stepping stone to make a malicious hacker's life harder.
They have everything they could want from your site, but presumably your site isn't a financial institution. The goal of most hackers is to crack relatively insecure or low-value databases in order to leverage the results for hacking user accounts in better-protected or higher-value databases.
