"The Black Ops 3 PS3 and Xbox 360 versions will feature Multiplayer and Zombies gameplay only, not Campaign. The ambitious scope of the 1-4 player coop Campaign design of the PS4, Xbox One and PC versions could not be faithfully recreated on old generation hardware."
that is a quote from activision. there just being lazy and don't want to take the time to make it on last gen. I guess that sucks for people with last gen consoles.