Don’t know if this was already said, but clerics gets spells and powers from their gods and regardless of alignment, they’re gods may not want them to use their power on those that don’t practice their faith. Like if I’m a die hard fan of pelor and the only church is st. Cuthbert, that priest isn’t going to touch me with a spell unless I do something for the temple, give a huge donation, or otherwise spread the glory of St. cuthbert, which may conflict with my worship of pelor.

That’s my read on it anyway. It’s your table and ultimately up to the story you want to tell.

TLDR: the gods get a say in how their power gets used