Yeah, You have to really flesh it out for it to be viewed as anything other than a tax. Some ways to get around that...

There's a pantheon, and each player chooses whom they tithe to. There could be tithes of coin, of service, of blood, of gems, of wine, of bones, et cetera; each with a benefit, which could be anything from "free healing" to "free blacksmithing" or "weapon insurance" or "cheap consumables". It's not just "because reasons", it's just built into the system that gives them meaningful choices.

Make it a genuine game mechanic. You don't pay the tithe, suddenly the clerics become hateful (Spanish?) inquisitors in the night. Basically, they're a higher-level-then expected dungeon in broad daylight that you can buy your way out of, with the low low cost of not knowing that ahead of time.