They'll never add it since Halo fans would lose their shit even though it would fix so many issues that Halo has had since 2004.
The issue with drop-in drop-out matchmaking was that it fucked with some of the core systems in play:
1 - Games would start with uneven teams far more often than other games under the assumption that a player would join mid-game, and then there was a decent chance that never happened.
2 - It was possible to be placed in a game that was hopelessly lost, even after patches that were supposed to mitigate this.
3 - It was possible to be outnumbered and never receive another player on your team because you were losing so bad, leaving you in a situation where you have no choice but to lose or quit.
4 - It was incredibly easy to game objective gametypes in to Join-In-Progress murdermills where you could get well over 100 kills over the course of the match (shoutout to Lightning CTF)
This happened often enough to leave the community disgruntled.
And LAN wasn't a huge part of the Halo community?
You're asking the wrong question. What you should be asking is whether or not Microsoft/343i
cared that it was a huge part of the Halo community.
