Why? Seriously, it was a really fun mode, why did they remove it from matchmaking? Add it back. And for permanently this time.
“Reasons”
Same thing will happen with Fiesta when this event goes down Tuesday too sadly…
Fiesta is now a permanent gamemode, has been for a while now….
Attrition has been confirmed to come back in the future.
The gamemode was a event exclusive mode but as previously stated by 343 - event modes like attrition will find their way into the game in a more permanent manner in the future.
So why not make it a permanent mode as soon as the event ended? Kind of dumb to just remove it from the game to add it back in later “just because”
They probably do some adjustments and fix any bugs while it’s away and bring it back later.
https://twitter.com/RevivedAntihero/status/1488587286342111232?cxt=HHwWgMCsuYCQw6gpAAAA
'Hey Spartans!
- The team is going to bring back Attrition in a more consistent manner such as its own playlist or part of a new one down the road. *
Thanks for playing and providing feedback on its debut. We love the mode too and we’re happy to see such a positive response to it.’
What? You thought the game was actually going to let you play what you want to play? Hahahahah! The only thing permanent is the shop so get to spending!
ngl Attrition was prob my favorite casual gamemode. I wish it was available in ranked as well, and it should at least be thrown in the Quick play cycle, if not stand alone playlist. I get that it will be added later, but don’t really get the wait tho.
On top of that, is the achievement for 3 revives actually for this gamemode? I got 3 revives in a round several times without the achievement poppin, then again the ach says “elimination round”… just figured Attrition was the mode but who knows 
They’ve clarified this on twitter in the past & more recently.
Simply adding a playlist in isn’t just a flick of a button, if it’s been set to be a temporary playlist they need to adjust that on the backup to make it a permanent addition.
In addition to that, they also have a lot of community feedback on the mode that they may want to look at and adjust before they bring it back to the game.
A prime example of that would be the elimination circle essentially playing a useless role in the mode 99% of the time.
Just be patient my dude, I’d like it to come back to but being mad in a forum isn’t going to help. Wait like everyone else.
Considered the pc playerbase declining, they can’t add too much playlist/gamemodes.
Simple there aren’t enough players.
They removed Attrition because it was a pseudo-Battle Royale mode that everyone hated
Their original idea (as stated) was to use Events to test out new game modes that they wanted more feedback on. There is precedent of it then simply becoming a permanent mode with Fiesta - so it might happen. But for whatever reason they seem to prefer to gather feedback and then incorporate it behind the scenes instead of changing it on the fly with updates to the live game.
So that’s the reason. Whether or not we agree with it is of course something different.
Part of the reason the player base is decreasing has to do with limited playlist variety though. They’re helping cause the problem they’re trying to fix.
Was 343industries choice to rush the launch of the game.
On xbox they have a good amount of fans, so they can take time.
On pc halo series have already 3 fails, so playerbase was little.
They simple not cared, probably hoping f2p card will help them to bought some time.
Isn’t working.
Every action have consequences.
Ya remove a fun game mode from a dying game starving of content. Good job 343i just keep hammering in those coffin nails…
Probably removed it so they can add it back in in the upcoming content update (Feb. 14th I’m assuming) so they can say," Oh look guys! We added new modes!"
But in reality, the only “new” mode is KOTH
https://www.techradar.com/news/halo-infinite-is-losing-players-fast-but-thats-no-problem-for-a-live-service-game
Maybe 343 commissioned this article XD