Battlefield 3 and Call of Duty: Modern Warfare 3 both feature co-op campaigns. DICE decided to throw six missions and entice players to play it by locking some multiplayer weapons behind it.
On the flip side, Infinity Ward and gang created a completely separate offline only profile featuring its own set of unlocks and progression system. They didn’t dangle any carrots because they were confident that they’re Spec Ops co-op mode was good enough to stand on its own.
I picked up Modern Warfare 3 for its Spec Ops and a bit of curiosity with its campaign and multiplayer. I picked up Battlefield 3 for its multiplayer alone. I would have been glad to have paid full price to have them not include the co-op and its single player campaign.