Who said it was a dying sport? It's not as popular as it used to be and the average fan age is increasing. It's far from being a money loser or anything, the main point is that the sport of football isn't as hot as it used to be.
I don't think the sport is popular enough for people caring about non NFL or NCAA football.
It may grow as a niche but really why wouldn't Arena football succeed after all those years and investors, what makes XFL or AAFL think they can succeed when they have zero differentials from NFL/NCAA. It's just a vastly inferior product. At least CFL is a different experience when you watch.