A karmic backlash was a celestial's worst nightmare.
To become a tier9 individual, one had to gain experience and slaughter hundreds of millions if not billions of monsters to reach that level.
The reason behind monsters being the accepted norm for levelling versus bipedals was because killing a monster accumulated lesser bad karma than killing a Bipedal.
In the end, the higher one climbed the greater their karmic debt to the universe became and to wipe off the said debt they needed to perform several 'good' karma deeds which was the only reason why the celestials installed the universal queen into the universe, as her presence as a governor after the chaos war ensured that one-sided slaughter of mortals by gods to become stronger fast could no longer happen.
As a result, the universe became a more peaceful place to live-in and the celestials received a steady stream of positive Karma.
