Firmly Asserting: Peasants are Children

 If peasants were adults, they wouldn't need supervision. The issue is that peasant and below is about 99% of the population. 

 I believe the interruption of maturity comes from crippling deformity. Maturity attempts to complete but component parts are missing, so it crashes. Historically, this is due to the fact farmers outnumber hunters some 100:1. Who are the extra 99? Folk who should have starved to death due to crippling deformities. At best, the descendants of horrifying mutants. However, your enemy has to butcher their way through them to get to you, so you end up keeping them around anyway...

 Admittedly part of the problem is the coding/debugging.You can easily write code you cannot yourself debug. IQ clearly rose well before social complexity rose, making the average smart enough to innovate trouble they couldn't get themselves out of. Peasants create problems (and wealth), lords create solutions.

 However, even if an adult is smart enough to get himself into trouble he can't fix, he's mature enough to humbly accept guidance. At least to not to get himself into that trouble a second time. Peasants have no such affordances. Even when they're told how to avoid trouble they'll force the lord to yank their leash again. Idle (peasant) hands. Female peasants actively like getting their leash yanked and provoke it for fun, so they can humblebrag ("complain") to their frenemies about it.

 Of course lately population has grown even further, pushing the lord ratio to 1000:1 or thereabouts. This is beyond the Dunbar number, meaning no matter how efficiently allocated, there simply aren't enough lords to cover all the peasants. If there's been any anti-aristocrat selection (WW1) maybe it's like 2000:1. Some have tried to get better scale by homogenizing the peasants and broadcasting to them, but there are numerous issues...

 Part of the reason the pastoralists have been more successful in recent times is that pastoralism, while more populous than hunting, isn't quite the full zerg-rush you get with sedentary farming. They lugged around a smaller peasant class. Lower total mutation load.
 Without severe breeding restrictions, probably way worse than India, the former-hunter aristocratic class tends to blend into the clueless biomass over the millennia. Diffusion threat. Have to speciate by fiat if you don't want to have them drag you down to their level.