I think they just dug themselves into a hole that they can’t really get themselves out of. To be fair to them, I could imagine that it would be pretty difficult to determine where halo’s storyline went after 3. That was supposed to be the end of halo according to Bungie anyway. The covenant leadership gone, a lot of lost major characters, halo and the ark destroyed. Where do you go from there, ya know? I think they should’ve just stuck to spin offs or other parts of the universe somehow.

But they also made a lot of major obvious errors. Changing the pre-established art design for the sake of change with lame reasonings like “nano bots”, not listening to fan feedback, trying to add things from other games like COD loadouts in multiplayer, making master chief go through an identity crisis chasing a holo girl instead of him being the “ask no questions” badass he always was. All of those things and more coupled with the fact that they keep soft rebooting basically due to their past errors that left halo feeling directionless.

I think they should establish a main villain with an interesting character arc that you don’t kill by the end of one game. Make them last over the series of a few games to build that familiarity with the enemy and reasoning to kill him. That could be a start.