The only reason they agreed to do it again was because Kiro said they could ask a couple of questions they wanted to ask too. He didn't know why apart from After Dark they weren't more curious about harbingers. And that meant running the mountaining a couple of more times to receieve answers.
They didn't know it, but the more they repeated the process the stronger they got and the simpler it was getting to the throne room. The game system had deactivated their notification sound, so they wouldn't know when they level up.
It figured this was a good thing for them, for Asgard. And wanted to believe that, if they knew how stronger they were getting they'd get too arrogant and cut the training short.
Although Prometheus could've made his monsters much stronger, he waited until they were just strong enough and continued to whip out monsters that were just strong enough to challenge them.
