Strategy board games like Risk were complicated enough for most people. But some advanced players wanted games that simulated battles more accurately and in greater detail.
Wargaming became a serious hobby. Wargamers learned the complex games that had been invented to train military officers. And because they loved their hobby, they invented ways to improve the games they played. For example, some experimented with adding specific characters into their games, such as the mayor of a town near a battlefield.
Others turned to fantasy. Wargames often recreated battles from history. But the battles in the games could turn out very differently than actual historical events. That was part of the fun. Since the games were already imagining alternate versions of history (“What if the other side won?”), there was no reason why the players couldn’t imagine other fantastic “what if” details just for the fun of it.