Because most fighting games don't have the smartest AI opponents. If button mashing works against human opponents, either the game has a bad control scheme, or (much more often) the non-button masher just isn't that good. I can't think of a mainstream fighting game where non-strategic button mashing (i.e. actual mashing, not move spamming) can't be countered fairly easily.
It can be argued that Capcom themselve supports Button Mashing. At least one of the Sega Saturn ports of the vs. games (been a while since I've played, I forget which one(s) in particular) have an "Easy Mode" where you can enter special moves by simply hammering the buttons rapidly (no controller motions required).
Play as Eddie Gordo in Tekken. That's a character where button mashing works to Game breaking levels.
Mashing is only really effective against mediocre players and is easily countered with projectile spam. Mashers rely on accidentally using special moves and being unpredictable and random. If you keep them away and spam the beams and assist beams, they won't be able to hurt you and you'll disrupt most of their supers. Even if you don't projectile spam, if you have a grasp of basic combos and basic defense, you can just sit and wait for them to do a move with a couple of frames of recovery and punish them. Patience will win the match.
Speaking of Easy Mode, why just have easy mode make the controls easier? Why not just have simple controls from the start? Isn't intentionally making controls a hassle Fake Difficulty?
Difficulties in controls in fighting games are usually for the sake of balance: should a grappler be able to use his high-damage grab specials and supers whenever he or she wants, or only when he manages to fit one or two full 360 spins alongside several other button presses in the span of a second into regular combat? To expand on this, complicated maneuvers for moves are usually to make it difficult to spam them and to put additional thought into how to retaliate.
Also, easier controls for performing special moves can sometimes come with losing other moves: Marvel vs. Capcom 3 is an obvious example. In order to give space it assigns all of the "normal" moves you can typically access at will to a single-button auto-chain, meaning that you effectively lose the other moves unless you chain into them. Essentially, with limited buttons and a whole bunch of moves, some of them naturally have to be relegated to alternate motions.
Joe, Zero, and Karas all have Yami in their UAS ending.
And, in Ultimate All-Stars, we find that he was manipulating reality.
Still on that specific game; the simplified controls for the wii version just bugged me. It took a lot of the mastering difficulty out of the game and allowed for spamming, but not button mashing. Also, there wasn't an all character move list, so I was never able to figure out the inputs common to all characters. Next, when you assigned two in-game buttons to one controller button, it did not always (read: almost never) use the attack used by pressing the buttons at the same time. Finally, the online play had just enough lag to change the controller input speed for combos, so all the time training offline was almost worthless in an online match. And another thing! The points ranking system was so wonky: the first time I played online, I faced someone in the top 11 rankings. This game just bugs me! /rant
Who do people call Public Medium Ignorance on Tatsunoko vs Capcom because they don't know the anime characters but not on Marvel vs Capcom? Few non-comic-geeks would reconize Onslaught, Marrow, Shuma-Gorath, etc.
Because the Marvel side still has loads of characters that are far more well-known than any in Tatsunoko (or in Capcom for that matter). They outweigh the obscures on their side.
Mention G-Force in passing. If Americans recognize the name, they will refer to the 2009 Gerbils as Secret Spies Disney flick. Meanwhile, people may not know Onslaught but they know who Spiderman and Wolverine are.
This American troper watched G-Force as a kid and resents the generalization. *shakes fist*
Because Volnutt and Tiesel aren't around to appeal to her nicer emotions.
Who's bright idea was it to put in more Darkstalkers characters in Marvel vs. Capcom 3 than Mega Man characters? I mean...what? The worse is that instead of trying to put in somebody other than Mega Man Classic...they just left him out. Likewise, why Hsien-Ko out of the other Darkstalkers? Morrigan is the main character. Felicia is the main hero in the Cartoon series. Hsien-Ko...is just a demon hunter. Note that Marvel vs. Capcom 2: New Age Of Heroes had loads of characters, so including some from other series wasn't a problem, but she just...doesn't have a reason to be there except for a very odd kind of fanservice.(she's undead, folks)
The fact that Darkstalkers is a fighting game may have factored into it.
Still doesn't excuse the lack of the Blue Bomber himself, though. You know, the main character of Mega Man itself.
Simply put, they have some problems of making his moves. Making movesets, you know, are not that simple. There are many things to consider.
Hsien-Ko brings more than just "fanservice", she brings more variety with her unique moveset than Mega Man would. Plus, I highly doubt that being the heroine of the cartoon would justify putting Felicia in the game, seeing how both Capcom and Darkstalkers fans pretend that it doesn't exist (unless to make fun of its cheesiness), and the fact that Hsien-ko was a main character/deuteroganist in the far more well-received anime. The reason Felicia made it in was because of her popularity as a character, and the same reason applies to Hsien-Ko, as though it may not be big as Mega Man's, she does have a fanbase who wanted her to return to a game for quite some time. Though to be honest, even I'm surprised that she made it over Mega Man.
Headscratchers is definitely not for discussing that kind of things, but I'll give my opinion on that. First, smaller roster compared to MvC2, for the sake of the balance which previously was broken to the memetic extent. Second, the quantity of the Mega Man installments compared to the Darkstalkers' (might be the reason why Jin is in MvC1&2, even though the series are more popular in USA and Cyberbots were not quite a hit game there): Mega Man got like three or four universes, each having about ten parts (and that's not ciunting spinoffs); Darkstalkers limited itself with three parts, extended only with updates. Third, Hsien Ko and Felicia also have a considerably big fanbase and weren't showing up as actually playable characters for a long, long time.