To be fair, Reach does this, just not ideally. Or maybe it does.
There's too many factors that are unknown to us to say. What we do know is that we only get the DLC maps very rarely unless we go into a DLC required list, but those kind of suck.
My thought is that the searching requirements are too loose. It puts time as the top requirement for searching. So it starts out looking for players similar in rank, location, and DLC. If it can't find them in X time it lowers the priority of those and we need up with what we have now.
The searching parameter things we have control of help, but they seem to be just soft rules. I wish they were hard and more enforced so if we chose to search by skill it'd actually do that. I'd be OK waiting longer if I could choose to search by DLC, skill, no guests, and location. If I could turn all those on and get perfect matches that'd be great. I'd guess that matchmaking would take forever though and I'd have to turn a few off. Perhaps Bungie already messed with this and found the most ideal settings for getting us matches even though we don't agree. Maybe there's just not enough people playing at a point in time to make this work perfectly. The thing CoD has is that all players can be matched together right? Skill doesn't matter?
Still, I'd hope that searching can be tightened up a bit. Anyway, my thoughts.