>>724135760 (OP)
Multiple layers of reasons honestly.
Smash has both unique and polished mechanics, even at its lowest point with tripping nothing came close to it.
Actual effort from Hal, Sakurai and the devs to make all the IPs blend and mix together, is not Fortnite that just throws shit at the wall to see if it sticks, Smash legit feels like a celebration instead of a product made by comitee.
The competence did absolutely nothing for 15 years. Sure with Smash 4 and Ultimate clones became a common thing but every company had the chance to try something during the 6th generation and no one did anything beyond that TMNT game, Viewtiful Joe and that weird Konami game, why no one tried to do an Smash clone with an original cast for th3 ps2?
Mosr IPs that get in Smash get a lot stuff: characters, items, stages, movesets, music, assist trophies, stickers and so on. Not even Multiversus could compete in that regard