It's a combination of two things: poor management and contract work mandates at MS. According the this article, management was horrific, people were working in such a way that there was no communication between them, and they were essentially making 5 games at once, when they all came back together, the pieces didn't fit, and in 2019 2/3 of the content (if not more) got cut and the game was basically soft-rebooted. This is a management problem.

On top of that, you have a contractor problem. 343i relies on a lot of contractors, which is not uncommon in the gaming industry, however, MS has a company wide policy that contractors not be given contracts longer than 18 months. That's basically enough time to get used to the system and rush out a few product, then the next contract has to come in, figure out what the previous one is doing and how their systems work, so they can add to it. Add this up over 6 years and spaghetti code might be an understatement.

Combine these two issues and you get what we see now. Rushed code that almost assuredly has small cracks in it that would pass a rushed inspection. Now the full time employees have to crawl through all of this mess and make sense of it. It will take a long time before 343i is able to produce content at the cadence that we want them to. In a way, given all the issues, it's a miracle that the game is as good as it is.

I don't have anything against Bonnie Ross personally, but she is at the top of 343i, and has had 10 years to right the ship. Instead, the mismanagement problems at 343i have only gotten worse with each release. As much as I like Halo Infinite, it is almost literally painful to imagine what could have been if this game was managed well. 6 years and an unlimited budget, it could have been an absolute masterpiece. Imagine if it had more varied biomes, different dynamic events where the banished actively do things against you, large scale battles including tanks/scarabs, dynamic weather, etc.,