@kayriel nah, the mere fact that the phrase noblesse oblige has the word for nobles in it, goes to show that the concept is an ad-hoc construct made retroactively. Nobles are simply the people who, usually through force-of-arms, put a territory under their command. Allowing them to tax their subjects and conscript them into their armies (its not banditry if there are no laws against it!).
Granted, that is only half true, and the other half of it is that there are ppl granted the land by someone else. To keep the region pacified for them while retaining a share of the taxes and ability to call upon arms.
That said, it does make sense to use some of the spoils to develop the region, to increase future spoils and keep the populace from doing costly riots.
@HDMI1 it was not just a friendly competition though. There were bets riding on it (including one about making a girl his mistress iirc?), and economic decisions, and whatnot. But even if it were, it only makes sense to ensure that the aristocracy are the ones to gain the "honor" of "winning". Not like the commoners are in a position to complain.
As for trusting with management, I think moral incompetency has very little to do with incompetency at management. However, when moral bankruptness (the kind that doesn't touch the taxes sent to the superiors. If that happens, its time to off their heads!) results in plans that are exposed, that suggests incompetency, which is a reason to consider replacing the guy. But merely a single time can just as well be due to chance as it would be incompetency, meaning it smells more like an excuse for some superior already looking to get their hands on the title and territory to give to someone in their faction/family.