why does everyone take that as a fact
HE loving SAYS "IT'S JUST A THEORY!... A GAME THEORY!"
It's taken as fact because there hasn't been a theory as popular as that one.
Although I don't often agree with Game Theorists (because they're loving theorizing stuff from GAMES), there's really not much of an explanation besides theirs for Pyro.
Unless you've got a better idea. Hm?