Becuase they don't have any major gimmick, making the first game of a set as fair as possible. Imagine if whoever gets to stage strike last could choose Pokemon Stadium 2.....
"Major gimmick"? Okay, first of all, what does that even mean? Does Omega mode count as a gimmick? It's the only stage in the game with no platforms. It makes it so much harder to approach certain characters. It makes it way harder to deal with Little Mac. Why doesn't that count as a gimmick? What do you mean by "gimmick", anyways? And can you really still call it a "gimmick" when it applies to
all but 3 stages in the game? That's not a gimmick, that's a given.
What's more, most "gimmicks" are either matchup-dependent (such as a pass-through floor), in which case they will be struck if one party considers them worth getting rid of; or
knowledge-dependent (such as knowing not to carelessly approach a Robin who is walkoff camping on Delfino - for all intents and purposes, Dabuz SD'd against Nairo in that set) in which case it's absolutely reasonable to give a player an advantage for knowing more about the game and understanding it better. To take your example, Pokemon Stadium 2, every element of that stage can be plotted out and worked around. It's liable to provide an advantage in certain matchups, but
those matchups can strike it. Just like people can strike FD against Little Mac or Toon Link. And furthermore, none of the "gimmicks" are gamebreaking or would lead to the worse player winning. You can learn to deal with the conveyer belts. You can learn how your character works in response to lowered gravity. You can learn what tricks you can abuse on ice. It's all about
knowledge. That's not a gimmick, that's a feature!
You apparently don't see a problem with PS2 in game 2 or 3... Why? Are those games somehow
less important? Personally, I think PS2 is perfectly legitimate regardless of which game it is in the set. But if it really is a gimmick which hampers competitive play, why allow it for games 2 and 3?
Look man, I get it. I understand but the game isn't neutral. Nothing is really neutral but this is the closest thing to it.
Actually, in Brawl, FD was one of the most-banned stages. This seems to imply that not only is it not neutral, but that it doesn't even come close. What's more, SV was the go-to counterpick once FD was banned, which would imply that it, also, was not only not neutral, but didn't come close. Because each stage is different, and each stage favors different attributes. A character with an amazing ground game
loves FD, because the only times he has to take to the air are when his opponent forces him up there. By comparison, on BF, he might have to hunt them down on some platforms. A character with a lousy ground game is gonna love, say, OGA*.
*On a side note this is a shockingly good Little Mac stage. No, seriously. Small blastzones a lot of the times, spots with very few places to fall off the edge... It's not half bad.
Because it's literally a level playing field.
Yes, but that doesn't make it an even one.
Part of the integral design of the game's characters involves how well they can adapt to different environments. A character like Little Mac is worse for his inability to cope well with platforms and various layouts. A character like Fox is better for his ability to cope with a large number of terrains. And when we limit the starter list like that, we
nerf that attribute. We artificially tweak game balance in favor of characters who are good on a very certain, specific terrain, and against characters who are good at a wide variety.
Yeah, Little Mac is
really, really good on a perfectly flat, even surface with no platforms. That "level playing field" you mentioned earlier. He
excels there, and can go toe to toe with most of the cast there. But that's not the extent of Smash. Smash has exactly two of those - Final Destination and Bridge of Eldin. By comparison, counting only stages that are legitimate for tournament play, there are something like 5 stages with pass-through main platforms, 4 stages with the delfino-esque "stop at various locations" gameplay, numerous ones with temporary or permanent angled terrain, at least 2 with damaging hazards, 2 with water... You get the idea. This "level playing field" is actually a specific outlier
even within the drastically reduced tournament environment! To use that as your baseline for "even play" just seems silly to me. Especially when it leads to some characters getting their second-best stage on game 1, the game which is supposed to be held on "neutral" ground. You're far better off striking from the list - you'll never get a character getting their second-best stage game 1, unless the players both agree to it. You'll end up with their 5th-best, 6th-best, or even 7th-best for
each character (depending on how big your starter list is), which, unlike SV, is actually going to be really close to "even" ground in almost every matchup.
'd already but there is a thread on said topic 
