I posted this not so long ago and suggested that the bulk of ttrpg players/campaigns are D&D and then a tiny percentage of the hobby is “everything else.” The notion being that  the vast majority of people who have ever played a ttrpg have only ever played D&D. There is the hobby of playing D&D and the hobby of playing ttrpgs is a separate category.

I haven’t played online much and was only recently aware that the Orr Group, which owns Roll20, publishes a ranking list of games being run on their platform. As might be expected by my hypothesis, D&D 5E is roughly half of all the games being run on Roll20. If you were to add all the earlier editions and OGL variants into the mix, its probably closer to 70%. While not necessarily a verification of my theory, I think it does suggest that I am broadly correct with the assertion.