The reason wasn't some operation of the undeserving occupying a position, it was a very simple reason...
The level of the Dungeons handled by Cardinals was vastly different from the level of Dungeons handled by an Archbishop like him.
With Sipher Archbishop's strength, if he insisted on dealing with those Cardinal-level Dungeons, the final result would probably be pulverization!
This world was just as cruel as that. If you didn't have the capability to resist the incoming dangers with your own powerful strength, you would be eliminated without hesitation.
Thus, anyone existing in the position of Cardinal within the Earth Mother Goddess Church was one of the top powerhouses of the continent.
So the question arose, even if these powerful beings, for various reasons, went into the "Coffin of Faith" ahead of time to sleep, handing over their power to the next capable successors, the average tenure of a Cardinal was at least 120 years.
