Great comment and those are excellent questions.
As we know there' s most often a cycle of abuse in these people's lives, perhaps they were abused or torture in some manner? By no means should this be an excuse to continue abuse but we see this time and time again.
Power corrupts, and people who start off with good intentions may be lead astray as they are often surrounded by people who have been corrupted long before their arrival. But we're all trying to figure out why the abuse of children?
I don't have the answers but I'm very intrigued by the possibility of Brownstone Operations being implemented.

Operation Brownstone, also known as a "Brownstone operation," is a reference to a theory that intelligence agencies, such as the CIA and FBI, engage in utilizing underage individuals for prostitution purposes with high profile targets, for the purposes of being able to blackmail those high profile individuals later. Generally, the incidents are recorded via videotape and the underage victims are debriefed after the encounter.

This theory offers the most plausible reason for systemic child sexual abuse, imho.