If that's the case, then we need to improve the AI a bit on that - I tried doing some improvements in that area a number of years back but was kinda crappy at programming and couldn't get it to compile so I commented out what I was trying to do - probably comments have been erased since then but maybe soon I can take another look at it. That said, some earlier AI versions would adopt a non-favorite religion but then if they GOT access to their favorite - and weren't TOO invested into the one they had adopted in the meantime - they'd make the switch. I'm not sure how they behave right now. National religious strategy does seem to be a place we could greatly improve on for the AI overall. Original Civ IV (not even BtS) Vanilla was better at it than our AI is currently.