This is a little frustrating. I downloaded the Champions pack and neither of the new maps have ever shown up in any playlist I have went into. Are they just really uncommon?
It has nothing to do with the maps being uncommon, since they are integrated into the appropriate playlists the same as all the other DLC. The problem is due to Halo 4’s low population and many of that population having no DLC.
For the DLC to show as voting options, EVERYBODY in the game lobby must have the same DLC as you do. If just a single person doesn’t have the DLC, then it will not show as voting options. Unfortunately this is the case maybe 90% of the the time since, as I said, the number of DLC owners is less that the number of non-DLC owners (meaning less chance of finding DLC maps).
It’s really just a case of developer oversight, OP. We basically gave our money for maps that we will play <=8% of the time in matchmaking.
That said, I’m down for some Pitfall customs if you want. Most of my friends have the map. My GamerTag is linked to my profile. We are hella-sweaty tryhards, though 
[NECKBEARDING INTENSIFIES]