Simply because multiplayer is where the meat is in these CoD style FPSs. Don't get me wrong, CoD4 singleplayer was amazing, I've completed it on veteran 3 times, CoD WaW's was solid, and even MW2's was passable. But its short as hell, you can run through all 3 in ~5 hours on normal, maybe add a couple for hardened and a fair amount more for veteran (apart from MW2). That is not value for money, unless you can get them cheap, which 9 times out of 10 means waiting about 6 months or so. MW2's spec ops doesn't have you coming back for a better score like WaW's zombie mode, which carried its ok multiplayer. Personally I've spent hundreds of hours on CoD multiplayer, I'd say I even got my dough's worth out of MW2 before I threw in the towel. So yeah I understand your argument but its completely misplaced when dealing with these kinds of games.