Do you think there's a reason games that DON'T use d20s as their primary dice are considered inherently more "narrative" than games that do, when as you say BOTH types create narratives, just different kinds? You've got me curious now about how the type of dice you select can influence the mechanics of a game and how those mechanics translate in turn influence the storytelling!
The shape of the dice has nothing to do with a tabletop roleplaying game’s baked-in assumptions about what sorts of stories it’ll be used to tell. It’s pure marketing; d20s are popularly associated with Dungeons & Dragons, and back during the early 1990s, a lot of other RPG publishers – most notably White Wolf of Vampire fame, though they were far from the worst offenders – decided it would be a bright idea to adopt promotional pitches that went something like “D&D is for stupid mainstream normies who just want to roll dice; come play our game instead, which is for Cool People who want to tell Real Stories“. Predictably, a lot of folks fell for it, and the tabletop roleplaying hobby has been dealing with the fallout of the resulting culture war ever since.
(Ironically, most of the games that advertised themselves in this way were not meaningfully less preoccupied with complicated dice tricks and long lists of cool powers than contemporary iterations of D&D were; the disconnect between what they claimed to be about and the rules they actually presented has become something of an inside joke.)
