I remember someone in some webtoon commenting about why the church is "always evil" in these stories and I think...
Religious zeal and divine magic power monopoly and authoritative figure over the entire land and trust in church activities......... to name a few.... those are all very easy reasons to use as plot devices to push forward the story. Like, super easy pick to get some conflict rolling.
Throw in a pretty boy/hot priest and it's like, a no-brainer lol