I would think it would be pretty obvious why theism is always the example used. Standard human in-group/out-group dynamics and similar psychological factors. Unlike merely being of a different religion (at least in the US) being an atheist often comes along with (even causally triggers) a certain degree of alienation from many others in society. This alienation drives atheists to strongly signal group membership when around others of their kind and gives them a strong need for reassurance that indeed they are the ones in the right not the majority. Additionally atheism is the sort of topic where people feel the situation is so transparent and clear there ought not to be any question about the conclusion.

As to the Austrian school of economics (or hell the public choice econ class I took in college that had us constructing proofs about which preference axiomitizations are equivalent with and without the axiom of choice) they are right in that pure stipulative mathematical exploration can sometimes be a useful practice even in an empirical science. After all what is statistical thermodynamics than a purely mathematical and stipulative piece of physics.

The issue is that to be useful you also need to have bridge laws (which often go unstated) that govern when it's reasonable to assume the model assumptions are good idealizations of the real empirical phenomenon.