If people didn't reset to 51-60, the queues would be even longer because you'd have people on 61-70, 71-80, 81-90 and 91-100. So everyone just resets to 51-60 so the most people are in queue making queues shorter. It's just better this way. And aside from the boss, all of the floors are basically the exact same garbage over and over and even the bosses aren't that unique.