I think about the
bandwagon effect, and the
Matthew effect, the inertia favoring the most popular brand. For example in a little city where most of players choose GW then the new players will not choose other titles by other companies because it is harder to find people playing that game. And D&D is very focused into the crunch, when in the internet age the metaplot is too easy to be spoilered, and you can find free "fluff"(lore/background) with the fandom wikis of videogames, movies, teleseries and comics. Here if a player wants to buy crunch, then they will would rather the system used by the most.
It is curious the case of Tormenta, a franchise by a 3PP with very good health after decades to be from a not English-speaker country. And the origin is an article in the Brazilian Dragon Magazine. I don't see it to be translated into other languages. Maybe WotC could offer some partnership deal like Exandria/Critical Rol.
Other factor is D&D to be ideologically neuter.
I wonder about a Japanese, or Korean, version of action-play game-show with virtual avatars.