Because I don't really give a shit about fighting games? I mean, some are fun, yeah, but I don't want to memorize long lists of moves, what works against what character, what is more effective standing or crouching but if they're jumping to the left, use this!, figure out my tier A B and C characters...fuck that. Fighting games are fun to play with friends in the same room. Which is why MvC2 is a blast. Insane amount of characters, ridiculously over the top, fast, silly and totally broken. It's great.
Also, unless you're a total fighting game nerd, you care more about Ryu beating the shit out of Captain America and Jill Valentine than...Christ, Mai Shirani? Did I get that right? She's the one with the tits and fan, right? Die hards may think it's a "better" game (and I'm sure that technically it is), but it's not near as ludicrously fun.