Sorry to get off topic. Game companies decide what they're going to do. Sometimes a weaker console just gets a "downgrade" other times it's more like a different game. You could ask why the Wii version has features that none of the other ports has and so forth.
It's easiest to just make one game and downgrade the graphics or remove features to port it to weaker consoles. Some of the structures are different or there's some other reason to just make a different game with some similarities if you can't re-create it exactly.
Honestly I'm disappointed that the PC version (which could have been the ultimate edition) didn't have any new features and didn't have the multiplayer that only the wii version got. And why didn't the Wii version of FU2 (the only one to have multiplayer options) have a totally different type of MP gameplay than either TFU or even the single player campaign? Variety? Who knows.