You think 343i had all this content planned, but wasn’t purposely focused on just yet until the story reached to that certain point? Rakshasha armor core and Breaker BTB map released went the lone wolves came out, stated that Breaker was only gained because of “downloading off of Irataus AI data”. The Mirage armor core released because of Spartan Dinh previously wore it, and the Bandit rifle appearance because it was gifted to our spartan in the cutscene as his signature weapon.
We even want infection, and its shown possible to make even in Forge now. But the official mode is being held back until the story progresses later on, as most of you should know. Its theorized that firefight probably wont appear until the Banished probably attack the base or something.
Could we possibly have received these old content sooner but for the sake of story content, these were fed slowly to us?