they dont release everything in every area, simply because of economics and financial risk. They want to make as much money off a game as they can so they release the games in the areas they think there will be a good audience for it. Just like how they won't release alot of the American FPS games in Japan, because Japanese gamers in general don't go for the FPS genre. Sure there are those there who like it and are hardcore fans, but not so much so that a company is going to risk shipping thousands, if not millions of copies to the region only to have the majority sit on the shelves.
If there's a foreign game that isn't coming over, but we want it enough and make enough noise about it, the company will say "oh, they DO want this type of thing" and will most likely send it on over.