The FGC thrives on drama and that in turn makes certain matches incredibly hype. These rivalries, history, and storylines of actual players is completely disconnected from the mainstream. If someone who isn't necessarily apart of the FGC tunes into a stream, all they have to go on is the matches and the commentary, that's about it. They don't know anything but what is put in front of them. So they're missing a huge part in what makes these games so entertaining to watch.
The PL vs CDJr rivalry reached outside of the FGC. I had friends who don't like fighters wanting to watch them bout at MLG just because of the story and hype surrounding it. The match and game didn't even matter at that point. Eventhough PL got bodied 0-3, it was the hypest shit ever simply because it was apart of a storyline coming to a close.
I'm not sure how we can bridge the gap to where the mainstream gets ahold of these rivalries and background information, but this, imho, is something that could catapult the FGC into popularity regardless of whether or not the viewers have knowledge of the actual game itself.