One non-rhtorical answer might be,
" Because Church authorities, WHEN INFORMED, simply moved the offender to a different assignment, not telling the new parish/diocese of the probelm...again, and again, and again?"
IOW, in the one case, it was official concealment; in the other, when acts come to light, the offender is officially removed and prosecuted.
When teachers are accused of sexual abuse, educators and law enforcement authorities say, districts often rid themselves of the problem by agreeing to keep quiet if the teacher moves on, sometimes even offering them a financial settlement. The practice, called passing the trash, avoids the difficulties of criminal prosecution or protracted disciplinary proceedings.
"in the other, when acts come to light, the offender is officially removed and prosecuted."
I wonder. We see some prosecution, but then, we've seen prosecution of priests, too. I wonder how much is covered up in the schools.
Back in the 60s, when I was in high school, there was a photographer who had a little shop next to the theater where lots of people hung out on Fri and Sat nights.
One day he just disappeared. The word was that he had tried to put his hand on the wrong boy, and got a quiet visit from someone who convinced him that his best chance to see another birthday was to disappear, pronto.