How come when I play a 4 player game with 4 controllers plugged in, that it requires us to all use the same controller!

Because Codemasters (and probably Majesco followed suit) decided that we should all share the same controller and pass it around the room "hot potato" style.

Unfortunately, there's no way around this.

Bad decision. :(

lol, i dont mind....cause then no one can touch YOUR controller and say "ewww your hands are so sweaty!" and also since at the begining of a match u never know whos gona go first, so we all grab the controller and say whos gona go first eheh me? you? him? her? whos it gonna be? whos gonna go first? whos it gonna be whos it gonna be....im feeling it....its gonna be me OH JOY! it is

I Go First!

Unfortunately, there's no way around this.
There is...

If you're on Xbox live, host a game with the number of local players and each different player has his own controller. (It's a Microsoft thing.)

Yeah, I know. Horrible. Horrible. Horrible.