They usually seem there as a way to go 'look at our multiplayer!', and then force people to play it. Sometimes this ends up being sodding awful multiplayer, or barren after 2 days due to everyone playing more popular games.
In the case of games that are obviously never going to have the multiplayer pull of CoD, Halo, Battlefield, whatever the current racing game is, it's a desperate attempt to drag achievement whores into a multiplayer section that, chances are, is only there because every game must have multiplayer now!
In the case of games that are obviously never going to have the multiplayer pull of CoD, Halo, Battlefield, whatever the current racing game is, it's a desperate attempt to drag achievement whores into a multiplayer section that, chances are, is only there because every game must have multiplayer now!