Exactly why it isn't a fighting game. I'm sorry. Holding A and a direction to ring out people after their health hits 200% isn't a fighter. Add in the randomity of items and it's basically a party game. Same with the Sony variation before someone uses that "OMG YOU JUST HATE NINTENDO" argument.
They're both intended for quick pick-up-and-play button mashing elements of five minute sessions.
No items. Fox only. Final Destination.
Two players. Move lists that aren't simple button mashing (of course, then we can argue if P4U is a fighter, but it is because while it has mashy AAAAAAAAA auto-combos there's other move sets to use and auto-combo is a crutch). No randomize in stages (sup item drops), no having to dash around to platform to stay on the stage to continue to "fight" (Sup Pokemon Parade/Celedon City?)
Basically fighters are where both players have an even chance with no randomity involved. And if your game has to have players stop what they're doing to platform to stay in a match, it isn't a fighter all IMO of course. Because we could say "well, button mashy move lists are in DOA" and while, yeah there's "PP->PK" basic combos and the like the parry system there is deeper than Smash's "fighting" engine.