Hiya!
Another grognardish curmudgeon here. Started Playing & DM'ing in '81 (?), never stopped. Closest "player mostly" was about half a year in the mid 90's, and about a year and a half in early 2000's (after returning from living/schooling in Vancouver for 2 years). Other than than...97% DM/GM.
Why are there 'so many' of us old fart DM's? I have a theory...
Back in "Ye olden day's of yore", playing D&D wasn't "a
game you played on the weekends" so much as it was a "
hobby you partook in every weekend with others...but 'worked on' just about every day".
The difference is pretty strong; it's like someone heading to a friends place to play a video game ever Friday night. That person is "playing a game", and might have their own personal controller. But then there are people who head to a friends place to play a video game every Friday night...and they have a dozen custom controllers, every console created since 1985, and a PC gaming set up worth $10k. They have a Steam, GOG and Epic game library consisting of hundreds of games. They do this every night, for fun. They read about games, read about game design, read gaming magazines and are subscribed to several gaming eMags/Sites. They enjoy "all of it", not just playing the game.
The first guy? "Casual gamer". They want to just do something and have fun. They don't want to 'work at it', because that's not fun to them. The second guy? "True Gamer". Video games are his/her hobby, and they enjoy doing all that 'other stuff' and spending the money, because to them, that's fun.
For us RPG'ers, same thing. The older crowd like me think of RPG's as a "hobby" and not as a "game". A person with a hobby will spend endless hours in pursuit of that hobby, and spend hundreds, thousands or TENS of thousands on that hobby. The person who sees RPG's as "just a game" isn't invested because they don't really enjoy all aspects of RPG's...they just want to hang with friends, roll dice, and eat munchies. When not doing that, they are doing other things (like constantly checking their social media because... reasons... or something...

).
Anyway, that's my 2¢ on it. The Old Guard are STILL playing, spending time, creating, and DM'ing because that was the draw of the game back then; it was MUCH more "hobby focused" than it is today. Newer games and Players/DM's don't have that same drive (for the most part, at least
IN MY EXPERIENCE). I'm guessing it's mostly because there are soooo many other, easier, bite-sized-chunks of entertainment (re: youtube, forums like this, mobile games, social media, etc) that, well, they do that instead. It's easy. It takes little to no effort and can be picked up and put down at a moments notice. What does that say about society? Well, that's a WHOLE other kettle of Khargra!
^_^
Paul L. Ming