We cannot use DLC due to Microsoft's security and licensing system. If it was as simple as downloading a Map Pack, it would be a no-brainer. Also, the "MLG could get maps for free or at the very least heavily discounted" is a huge assumption.
I'm going to give a full explanation of why we can't use DLC. If anyone has a reasonable solution that we have not thought of, let's hear it.
Xbox DLC has 2 licenses. 1 license for the Xbox the DLC was originally downloaded to and 1 license for the Gamertag that purchased it. This means, the Xbox the DLC was originally purchased on, will work for all profiles on that Xbox. Also, if the gamertag that purchased it is on a different Xbox with the DLC downloaded, it will work for that gamertag.
Since we need Players to be able to use offline profiles, we need the DLC to be licensed to each Xbox. This means that the DLC needs to be purchased and downloaded on every Xbox. It also means that we need to make 250+ Xbox Live accounts to download the DLC. If the DLC is free, like we saw with Foundry, it just requires a lot of time to do it. For Foundry, 4 staff members (me, Nexy, Lenox, Synide) went to the MLG warehouse where we store the Xboxes for 4 days (~15 hours each day) and created 250+ XBL accounts and downloaded the Map packs. Also, something to note, is approximately 20-30 Xboxes would lose the Map Pack license every event. This would happen when hard drives would get removed and I would expect from the Xboxes bouncing around in the trucks during transit to and from events. When this happens, we need to create another 20-30 accounts and redownload the Map packs, usually on the Thursday before the event.
So that's free DLC. Now, when it's not free, here are the new issues. We cannot put the MLG credit card on 250+ accounts. Even if Xbox and American Express would allow us to make 250+ charges, we wouldn't want the credit card saved to that many accounts on our event Xboxes. 2nd option is getting 250+ DLC codes from Microsoft. We have tried several times in the past with no luck. Not only do we need to put them on each Xbox, but we need a lot of spares for the 20-30 Xboxes each event that lose the Map pack.
CEA is a new issue. Unfortunately, the Reach Maps are not on the CEA disc. Once the CEA disc is loaded, it wipes out all recent game history from Halo Reach. We use the recent history for selecting Maps and Game Modes so that all competitors can create profiles and access all the files. This means swapping between discs is not an option. However, an option we do have, is using only the CEA Maps and none of the Reach Maps. This means we would lose Countdown, Zealot, and Forge World.
I hope this helps everyone understand why we cannot use DLC or CEA Maps at this time. Again, if anyone has a solution we're not thinking of, I'd love to hear it