As a D&D child of the 70’s and 80’s, I’d never questioned the rule of the DM. It’s our shared game, but the DM is the glue that holds it together. The DM makes up the adventures (or prepares the published modules) and runs them, adjudicating both the players’ actions and what response the adventure has in store for them. Players know the rules, but don’t have perfect knowledge of how those rules are applied in the game world for any particular situation. In other words, the role of the DM is to rule.
But that’s not necessarily true these days.