Because the Arcade era is dead and there are more options for multiplayer games than ever before. In the past, fighting games were THE multiplayer games, maybe asides from side scrolling beat em ups like the Simpsons/Ninja Turtles games. Yes, games like Street Fighter and Mortal Kombat were very popular on consoles as well, but it wasn't the same type of culture you have in the arcades where people are gathering around and challenging each other. It feels like we haven't had much innovation when it comes to fighting games. It is still very much just Street Fighter 2 but with a different coat of paint. And that's alright but...they may have hit the limit of what they can do to change fighting games.

Street Fighter 2 changed everything. It essentially created a genre. In a similar way, I would argue Smash Bros Melee was a SF2 in its own right as it changed the perception of what a fighting game is, something still argued about, and it wound up creating a bunch of clone fighters in its style. You need games like melee, street fighter 2 if you really want to bring in more players. Something that reinvents fighting games in a way that can appeal to a ton of people.