I’d add Halo 4 to that list. I think people just lost interest in the series over time in favor of new ones that have popped up.
I didn’t really like the story in 4, 5 or infinite all that much. I honestly don’t like most of the multiplayer maps in the newer games either. I don’t think the new games are terrible but ever since Bungie left they don’t have the same charm to them. Like Halo 2 seeing the scarab for the first time, or the different locales on Halo you’d travel to in order to unravel the mystery of the ring. In infinite you go into a bunch of nondescript towers as Cortana speaks gibberish and the brute guy keeps monologuing at you repeatedly. It was just obnoxious.
It depends on the game. Like if it’s an online only game, then of course that makes sense. But a single player game, or even a game with a single player mode requiring always online is and will always be dumb.
Diablo 4 not being designed for offline solo play as well (like D2 and I think even D3 was) is annoying though.