Its a play on the word Monotheism:
Mono = One, Single
Theism = the doctrine or belief in the existence of a God or gods
Substituting Model with Mono we get
Modeltheism: the doctrine or belief that a model is irrefutable and stands over all others, to a point where the model user becomes dogmatic and defensive when shown the inconsitentcies and flaws of that specific model.
Coined by Robert Anton Wilson