An important aspect of the success of D&D/40k has been fan creations and lore explainers. A challenge for growing a creative commons (alternatives is that there isn't a unified set of "cannon" stories for independent creators to make "TOP 10 WACKIEST THINGS IN [franchise]" which are the intellectual equivalent to baby food (which I don't mean as an insult).

then again, d&d and 40k are popular because the companies that own them decided to let smaller creators do the work of reprocessing the decades worth of lore into easily consumable and marketable chunks. Both the small creators and the central company got to symbiotically feed off of the brand value of the other. Then begins the enshitification once the brand reaches the mainstream

The problem for less centrally controlled media isn't just that there isn't decades worth interconnected lore within one overarching franchise, it's that stories that aren't centrally controlled will mutate and be remixed too much to have the sort of symbiotic brand growth of 40k and d&d