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?