Hey bro i did the same thing, i have no clue why they dont BUT theres a way to play on them BUT only for zombies ok Steps:
1.MUST have your "bros" acount on your xbox
2.must have "TWO" controllers
3.start up black ops on your account then go to zombies sign your secondary controller in o your "Bros account it then press a two play with secondary controller and then press b on your Controller
it should kick you out to the main menu take secondary controller Bros controller/account press start it willl ask you to load it were ever zombie maps are saved to then go to zombies still on 2nd controller press a on 1st controller then sign 2nd controller out if it kicks you to the main menu press start on 1st controller go to zombies the sign your 2nd controller out and turn it off and there you go MUST do prosses every time you get on and cant go to online multiplayer to play like FFA SnD TDM or else it will erase the prossses that you have done
try this prosses on multiplayer and see if it works :p hoped this helped you.
-katxkiller

oh and btw if your bro get on you wont be able to use the map packs but you can try AND FYI im trying to figure out how to save it so you dont have to do that prosses every time