I consdier DnD a generic game for playing most types of fantasy. I can play modern urban fantasy, star fantasy, classic dnd, romantic fantasy, fairy tale, fantasy Leverage, etc in dnd no problem.Inspired by a question somebody asked on Twitter. My response was that every system feels different and provides a different play experience. You can certainly make most any system do anything, but playing Call of Cthulhu with the Mutants & Masterminds rules is going to feel very different to CoC with the CoC rules.
Every game has it's own niche and just needs to serve that niche well.
In the last year I've run: D&D 5E, WOIN, Pathfinder 2E Playtest, Ghostbusters 1980s RPG, Call of Cthuhu. Some for longer than others (Ghostbusters was just a couple of sessions, and we only got halfway through the PF2 playtest because the playtest schedule was so fast). Each of those games feels very different.
So why do you play games other than D&D? What is it that your game of choice does that makes it the best fit for the stories and genres you're playing with?
But for some things, it just isn't going to do a great job, and someone built a really rad game specifically dialed in to that specific thing. Like The One Ring. I appreciate the 5e conversion, but I'd rather play The One Ring proper, because it just does a better job of playing like I'm in Middle Earth. There are things that are hard to translate.
Or, I just don't want to play fantasy at all, so I grab a different game so that I'm not building half a game from scratch just to use the 5e engine.
Also a lot of the games out there are fricken gorgeous!