They aren’t trying the same account multiple times. Well they may be conincidentally (if the user uses a unique password per site and has been breached from multiple sites so appears in the breach list multiple times with different passwords) but not that frequently. What they are looking for is the intersection of users who reuse passwords and have been exposed by a breach and those users who have created an account on your site reusing the same password. Which is perhaps not surprisingly a relatively large percentage of your users.