Have you ever wondered why Microsoft has limited your number of friends to 100? Is it because they figure gamers are loners who have no friends? Is it because technology is a mystery to them? Or is it because they are still nurturing an old system because people still want to use it? Obviously it is the second option... I mean, the third. Sorry.
According to TheFeed, an inside source at Microsoft has blamed the issue on Halo 2. Now, you're thinking "I haven't thought about that game in years!" You are not the only one, but there are a lot of people who still play, and still do it online.
In fact, it is the top played original Xbox game consistently. In order for Microsoft to change the number of friends you can have, they would have to end the original Xbox Live system, which would end support for a still popular game.
Microsoft's hope is that the release of Halo 3: ODST will slow the popularity of H2, and give them the ability to finally move on from an old infrastructure, as people will now have 2 next-gen Halo game choices. Whether this will happen depends on the quality of the game, and if it receives the same "eh" response Halo 3 did, we will never see a new Xbox Live.