What they have done wrong:
Microtransactions in MCC won’t sell nearly as much as people simply buying the full suite. If they gave MCC tons more content, get people interested in buying it and filling matchmaking up with players so that people can get a match within minutes, then MCC will just snowball into something huge.
Problem is 343 doesn’t know how to do that, and 343 also wants to support Infinite for years to come. They can’t possibly spread their resources to support both games, and so they are trying to make an extra buck here and there, even if no one is going to spend MTX money on MCC.
What they should have done:
Imo 343 has got it all bloody wrong if they wanted to ever MTX a Halo title. They should have gone F2P on MCC H3 MP and then release their Spartan Point MTX on it. Then charge DLC for Halo Reach, CE, H2, H4 and H3 campaign. Why F2P H3 MP? Because no one wants to really shell out money on a 12 year old game.
Infinite should have been fully Buy to Play including MP, and then you can build a population on Infinite with all the shiny new stuff, new progression grind to stabilize the community there first, so that people who are interested in the “New Halo Experience” will buy into Infinite with a community there waiting.
Meanwhile, the F2P H3 MP will keep having influx and reflux of players, keeping the matchmaking and population there healthy, and people who REALLY love the Halo experience with this will buy all the other games in the suite and that will spread the population amongst all the other Halo titles.