Yeah, those nephew were often illegitimate sons, but that just goes to prove that forced celibacy has never worked.

Depends what you mean by “worked”. It prevented the emergence of priest kings quite well. Not allowing legitimate sons puts a major crimp in anyone’s plans to turn a religious organization’s land into their personal property. See how the Teutonic order turned into Brandenburg upon Protestantisation.

The Pope was a priest king for centuries not to mention the smattering of Bishop/Cardinal led mini statesi n the HRE.