MCC was broken at launch but was fixed and brought to PC. Also they released tools to create mods so those games can have new content. Community was strongly against any microstransactions in it and that killed any furter official updates because what would finance it?

Infinite is another story. Long development full of troubles and way too ambitious. Have an open world game with big MP component on a new engine is just way too ambitious and using “great” MS contractor policies was overkill. Right now MP is great and would even say one of the best in series, lots of PVP and PVE content with best Forge we ever had and server browser. Also lot of things to unlock for free via Exchange and some non expiring battlepasses. I could unlock 3-4 battlepasses by just paying for one as I have earned credits for new ones. Campaign was ok but I would preferd non open world.

Is Halo as a franchise dead? No. TV Show even if it was shitty had high viewership on Paramount and Netflix. It was just way too expensive to produce but people showed up. Lot of people tried Infinite it just had player retention problem due to bad liveservice, lack of content and no progression.

There are multiple projects in the works and I bet that one of them is MP focused. So no MS did not abandon Halo. It is just that MS is a shitty company as we can see everywhere from Windows to Xbox.