I mean, Banjo-Tooie to Crash to Mario Galaxy are all very different games but they're all still 3D Platformers. Same thing with Doom to Overwatch to UT to Halo being FPSs. Metroidvania seems to cover a comparable range of differences within the same genre, it just so happens to use game titles to make up its genre name. I'm sure if we had more Zelda clones on the market, like Darksiders, we might end up with a genre with Zelda in its name. Everyone knows what the term means, so it makes sense to use.