it's just that religiosity is correlated with a bundle of factors that tend to imply conservatism, and that church events give you a ready-made venue for talking to other conservatives.

That is probably an important contributor to the phenomenon; there is a certain "social conservative" mindset. However, I think that religion leads to some social norms, such as the idea that it's acceptable to pick one's morality out of old books, which provide fuel to socially conservative movements and attitudes.