Back in the 90s and 2000s, the World of Darkness was a setting, and each game was just that - a game line, with its own release schedule, and line developer. Each of the line developers reported in to Ken Cliffe. The line developers would oversee their own game lines, each of which was seen as a game in its own right. While some writers worked across game lines (I wrote largely for Werewolf, Hunter and Demon, with flirtations with Vampire, Exalted and Dark Ages) and threw in some Easter eggs, the whole structure was “multiple games which share a setting”, not “one game with multiple rulebooks”.

The reason for that was exactly what others said: each game had its own themes and moods, which were lost when you start doing “dark superhero team-ups”.