Because the USA is a bigger country than Canada... than any other country in the world.... if a company announces they are expanding into say a small Asian country people will say, "oh, that's nice." -- But if they say theyre expanding into the USA people will say, "Oh wow, these guys are legit!"
Just the mindset of people. And overall there are more people watching pay TV in the USA. There's DirecTV, Dish Network, Comcast, Cablevision, COX, Time Warner, Adelphia, etc.