The most painfully obvious reason is processing. consoles just can't process the high end graphics of today with the amazing amounts of realism on four seprate screens simultaneously. It just can't work that well. Halo will lag a little, especially when too much happens at once,and it's graphics aren't top of the line. Good, but not top. The most annoying is you're limiting this to co-op. there are a nice amount of competitive, but the largest problem with co-op is it brakes the game. Have you done Halo on legendary with 4-people? It's easy street. Hell, i srewed around most of the time and made my friends do everything and we still had no problems. By yourself? Annoying bullshit. Then there's the money and lazy developers, but that feels more like a cop out. And to the people saying "the screen is too small", i say fuck you right in the gums. Screens are larger and more defined now then they've ever been before EVER. if i played 4 player split screen at my friends house on his TV, it's still larger and better definied then the TV i play on NORMALLY! So you people need to shut the hell up. It makes me sad that four player offline seems to be fading as a whole, because it's a lot more fun to play with my friends in the same room with each other then over a very alienating headset. the only offline 4-player that came out recently is Halo 3 and MW2... for shooters anyway. There is always Rock Band.