Like most things, TTRPGs have inertia. Now, if you’re an avid gamer then you’re already familiar with this. If you’re not, let me know explain. Games in the world of TTRPG live or die by how many people are playing them. It has very little to do with how good or bad a game is (although this is certainly a factor!), rather it is about the opportunity to find a group to play with. The overwhelming popularity of D&D’s 5th Edition has returned that particular title back to it’s status as “the” game. Is it the best game? In my opinion, no. Is it a good game? Yes, definitely. More importantly, it is the most well-known brand in the TTRPG world. In fact, even people who aren’t gamers probably know the name “Dungeons and Dragons”.
The power of D&D’s name recognition though is extremely important. I’m watching people flock to the hobby because of the popularity of the current edition of D&D. I love seeing all these people come to the hobby. It really makes me smile to see people enjoying something I’ve loved for over 20 years. The inertia part plays a big role here. It is easy to find a game of D&D. Lots of people play it, are familiar with, and are willing to break out there dice for a session of it.
Beyond that though, fewer games have that drawing power. One of my absolute favorite games is 13th Age. I fucking love this system. It is great! If you haven’t checked it out I highly recommend you do it. However, as a game that isn’t well known, it’s harder to get sessions going. Its just a much less popular game. The fact that is an ward winning game don’t matter. Branding is effective, and D&D is top dog. Thus, the inertia is behind D&D. The upside to this is that people can branch out and try other games after they’ve cut their teeth on D&D. This is only a good thing.