Seriously, does anyone here besides me play anything else? I've got four game stores where I live and can't find so much as one other player for anything that isn't D&D.
There are several threads on this over the last couple years. Some of it is time where I only have so many hours to play games and why would I take away from playing something I know I like. Some of it is cost in buying more books and such. Some is finding people to play with and DnD always has people to play. It is a circle thing to some extent. Why would I watch baseball when I know I like to watch football- that kind of thing.
The last session I was in was Monster of the Week (as a player; it's not really my kind of game). I also played Dungeon Crawl Classics recently, and the game I currently run (on holiday hiatus) uses the Level Up rules.
I guess my big question is: what games beyond WotC 5e/5.5 count as "D&D" to you? Everyone has a different answer.
I've played some Monster of the Week and run my own games A Minimalist Fantasy Affair (Embellished Edition) and Black Aegis (Redacted Edition) last year (the former is available on Itch and the latter is currently in editing).