He needed a magic system, one of his favorite books had one that would work great in a game. He took it.. Would he have done that if he hadn't read it? Or read it and hated it? Parsimony seems to be both.
But the point was, it wasn't particularly about its appropriateness for the setting, it was just about a mechanically workable option that provided some operational and tactical decision making. That's pretty much the definition of a gamist design decision.