Its 2012. #esports is so big now that there is major overlap between communities. Nowadays just about everyone has dabbled in every community. Unfortunately, because of particular divides, they have to choose one or the other; they can't go to a FGC and a smash tournament at the same time for example. This reduces the player pool for everyone, so I think on that level, there is mutual benefit to be gained.
And I mean, we're all big boys. Put us all in the same room, outside of the trolling and flaming of the internet, and make us work together to find a solution and things would get worked out. Time would mend wounds and that would be that.
Beyond logistics, fear is the major problem; Smash players are afraid the big bad EVO monster will take over their game and they'll lose their grassroots influence, eventually subjugated to a side-event or a legacy game like SF3, and FGC players are worried that Smash's numbers could potentially overshadow their own in time, and thus leech off all the hard work that went toward a tournament like EVO. Those are legitimate fears, and very probable outcomes, so its no wonder why nothing will and maybe should get done.