WaW, MW2, BO, and MW3 were probably cheap games to make. Most of the money behind them probably went to advertising. I mean, you are using the same engine and same gameplay. All you are doing is making new levels for campaigns and multiplayer, reskinning weapons, and adding some miniscule features. The only major new additions to CoD since 4 have been zombies and spec ops.
The rest is probably just barely a step up from forging new maps on a Halo game, only using more advanced technology. I guess since Activision knows it has a die hard fanbase, it doesn't really feel the need to compete so it has decided to go the cheap route.
I wish there was some way to open up people's eyes. The only way we are going to get a better CoD is if people stop buying it. That will either shut down the franchise or force it to innovate.
But, if people enjoy paying $60 for an expansion pack and another $60 worth for DLC maps per year, there is nothing the rest of us can do about it.