There is not really any reason for it to be in the game. It does not enhance the game play at all. The main part of the game is not meant to be about gore and people exploding all over the place. That is what zombies in 3arc games was for and probably why zombies was only ever 4 players and not ever more.
The gibbing from WaW added a small level of realism to the game. While no, CoD isn't known for it's realism I'd much rather gibs and blood over money popping out of people when you kill them... Kinda takes something away from the game and replaces it with something worse don't you think? Let me just mention zombies since you brought it up, an extremely popular mode in the Treyarch Call of Duty games. Zombies has gibbing. Would I be wrong to say that game play is enhanced by it? Take a look at zombies and what does it give you? Cool weapons, repetitiveness, an easter egg challenge, gibs. That's zombies in a nutshell. Would I also be wrong to say it couldn't improve multiplayer? No. I could actually be very correct.
They money became prevalent because of the payback kill system. Where you killed the person that killed you. it was a stupid addition to the game yes.
Gibbing would not improve mp really, it is not needed. yes it may add a little eww/wow factor for some but overall it is not really needed in mp.
zombies has gibbing because it has less players in a match to deal with, so there is less issues about system performance. Even on the x1 it would cause issues because of the new higher level of graphics and detail making the gibs even more gpu intensive to render and with a lobby of 9v9 and half of them being gibbed at any point in time that would be a lot of network data and rendering to deal with.
You can't say it doesn't improve multiplayer, a lot of people would disagree. Sure, people would disagree with me too, you're an example, but in saying it does improve multiplayer is far more accurate than saying it doesn't (As it can be toggled off in WaW and I'd only assume they'd add the same feature in any other CoD multiplayer experience with gibbing). As I said before, it adds a small level of realism to the game and a nice feature to include. Call of Duty has been dumbed down so much, it'd be nice to have something interesting and new; even if that new feature is an old one brought back. Sure, maybe the consoles won't be able to run the game if they added in gibbing. For right now however, you don't know that.