I think it's because that, deep down, theists know their god is a bunch of BS.
I doubt they'd agree their god is a bunch of BS but they sure know how to exploit the depth and generous spread of the BS at their disposal
Their ability to make and defend emphatic statements of faith depends entirely on the slippery uncertainty of their foundations.
Challenge anything they say and they can just dodge behind the shelter of some other biblical quote or piece of theological excusiology, or invent some brand new BS of their own right on the spot
Just recently I re-watched this old but awesome lecture by Sapolsky:
He gives a pertinent and useful description of the schizotypal personality, and the characteristics of the shaman - very useful insights into the human types and motives of the never-ending supply of theists marching against reason.