It is basically the same as Reach.. I had the map pack when it was released for 0 MS pts and the maps were constantly in the big team playlist. Now, since the maps have been revoked I have no idea how much the maps are rotated in, but one thing is for sure the DLC playlist usually only has ~1000 people playing in them. My guess is that not enough people have the maps now and that they are rarely rotated in the normal playlists.

Hope this helps a bit.