SF, like many other fighting games, is a title where strategy is emergent. Noone at Capcom told people how to play. People just played the game, figured out what worked and what didn’t. People under estimate how complex SF strategy can become. The first in-depth treatise on footsies was only written about 25 years after SFII was released. Westerners only started understanding the neutral game as a coherent concept about 3 years ago.
But even though very few people could articulate SF strategy in a comprehensive way, most players understood the concepts either intuitively, or through experience. That’s how they can say about new games “this game feels like SF”, or “this game feels like KOF”. It goes therefore without saying that there are certain gameplay and strategic elements that contribute to a game’s feel. If you remove those elements, can you still say it’s the same game? That’s the idea on a very high level. When you go down into the details it’s easier to see, but the debate becomes more contentious because people forget about the bigger picture, and because as I just mentioned, very few people are able to articulate the reasons even though they understand them intuitively.
The more straight-forward version is that Street Fighter is generally known for its particular strategy around the neutral game. The strategy originally emerged because you couldn’t just walk up to someone and start hitting them. There were no moves that changed your air trajectory, and their were no moves that moved you safely across the screen and left you within striking distance of the opponent. This is generally the way it’s always been, and it’s how footsie and zoning strategies emerge. And of course, these are the two main aspects of traditional SF games. The beauty of these strategies is that they are built on very simple ideas, but just like in a game of Go, no two matches will play out in the same way. That’s why it’s a bit disingenuous to say that SF characters are homogenized in their approach to combat.
So if characters have ways to bypass the neutral game relatively easily, people will say they “don’t have to play Street Fighter” (which is why many people hate ST Vega). Characters like this tend to have moves like advancing armoured/invincible moves that are safe on block, moves that change their air trajectories (dive kicks, burn kicks, wall dives etc), moves that negate zoning, etc. Their options lead some players to think that these characters don’t have to utilize traditional SF strategy to win, or maybe traditional SF strategy doesn’t work against them, or both. In other words, playing or playing against these characters makes some people feel that they aren’t playing SF any more.