People dressing formally at church is correlated to...what exactly?

[DemPGH]

I think it boils down to the fact that church, and certainly what you could call church culture, is very, very close to business culture, actually. So to dress up for church, or to at least go "business casual," and I'm not sure if that term is still popular or not, makes sense.

In any event, preferences like attire are always reflective of the culture that sinks itself into any organized activity, church being one.