Well it is because some, and I mean SOME games can not handle or simply be made on another console. Hear are some reasons why:
-The company of the console (Microsoft/Sony/Nintendo) buy the game and olny allow the makers of the game to sell it for there console, you it becomes exclusive.
-Some games can't handle the new console, such as the nex-gen games would not work best on last-gen consoles.
Things like that, also the people who make, well the ywork with things that best fit them, and there abblities.
yea i hear ya man. i wish i can get mgs4 on xbox and brawl on the xbox too. but then again, nintendo and the sony company will loose money from it and then they will not have that much money to make their own games. just think of it as (i dont know) if your having a competition with two other people to see who makes better cupcakes. then your recipe was great and then you share it with other people. even if they bought it from you they have other recipes that can make it better and you end up loosing money. not very smart to do so isnt it? this is the same thing with the gaming industry.
I'm also pretty sure, it's because the maker of the console made the game. Why would they sell it to any other company when they can get all the business to themselves?
Also, some third party developers(example: Bungie) have special deals with one or two console makers. That's why the Halo series is only for XBox and the 360(Bungie has had a deal with Microsoft for a while now).