Historically, it’s been alleged that some ‘celibate’ Catholic bishops fucked women. When the resulting bastard children grew up, they were rewarded with coveted Church appointments. If anyone noticed the apparent favoritism, they blamed the adultery on their brother, saying the appointee was a nephew (it: nipote) rather than the priest’s own illegitimate son. Thus the origin of the term nepotism.

Probably some of them had different tastes and realized that fucking boys leaves less evidence.