Though I don't own it, I can see so many fundamental problems with SFxTK that's putting it in the "state" that it's in now in terms of some of the lukewarm reception for spectating.
Too much health/too little damage causing time outs, and lack of immediacy or pressure in matches, which doesn't help considering a lot of players are already carrying over very defensive play from SF. Overall matches and sets take forever and draw out game length significantly. Gem system ruined by shoddy implementation (including DLC gems) with after-the-fact fixes coming to the most interesting part of the game. Gem system further ruined by a gross, unnecessary over complication of choices that is unrefined and has created further selection problems. Combos sit between familiar strings in SF and some crazier stuff in UMvC3, which may be a bit disorienting for some to get used to, or find entertaining. A slight, but not really predominant sense of "use whatever is good right now" mentality with character choices going on right now reminiscent of late MvC3/early UMvC3.
List goes on. The game is, fundamentally, something that isn't spectator friendly. And will continue not to be unless some fundamentals are changed, most of which is unlikely. Yeah the game can evolve and become more interesting, but the chance of picking up new viewers diminishes too as time goes on, gotta strike while the iron is hot. I give it a shot just like every other fighting game I spectate but it almost feels like a chore to watch.
