GCs often have relationships with the regional admissions officer. Catholic high schools are the bread and butter sources for students for Catholic colleges, for reasons that include fit and yield. In addition, the AO will be very familiar with whatever level of rigor the high school offers.
From the applicant’s end, four years of high school theology classes, which may be full of self-reflective writing, and extensive service make pumping out a supplemental essay for a Catholic college a piece of cake.