Obviously we don't know exactly what they're all working on
Kind of makes it hard to see how one can be critical if one also admits they have no idea what the studios are working on. The smaller projects you're mentioning, like Grounded or Bleeding Edge, were already in development when MS bought them. Personally I think it's a good thing that rather than canning what they were working on and make the developers shift to something else, MS put support behind them and let them release the games. There's nothing wrong with releasing smaller titles, all the companies do it, but it also takes years and years to make a AAA game and MS hasn't owned these studios for years and years. Plus many of the ones they bought were already in the middle of developing big titles.
Alot of these multiplayer focused games that review poorly, are just left to die a week or two after release.
State of decay 2, seems to have "stuck" around better (than crackdown 3 or Bleeding edge).
Bleeding Edge just came out and we know more content is coming. Crackdown 3 got multiple updates and is not a "MP focused" game. Having multiplayer doesn't make a game "multiplayer focused". State of Decay is even less multiplayer focused and it has gotten tons of post launch support.
I think its a bad strategy to focus so much on these multiplayer focused games, theres too many of them, most are poor quality.
Big AAA games from multiplats, do things so much better that these games are basically just fighting a loseing battle from the start.
Its almost unavoidable, that they just end up left for dead.
You just listed a ton of first party Xbox content and only three to four were multiplayer focused games. Some of the other titles have strong MP elements but also have strong SP. And a vast majority of the ones with strong MP elements got good reviews, and got great support post launch. So I have no idea what you're talking about here. I mean, you claim they release too many MP focused titles, most are bad quality, and a lot are forgotten with no support and "left to die a week or two after release", so let's go down your own list.
Ori and the blind forest - Single player
Ori and the will of the wisps - Single player
Gears 4 - Has MP, I wouldn't call this a MP focused game though. The marketing certainly went into the campaign. Either way, if you want to say this game is MP focused, it doesn't fit your criteria of poor quality, forgotten, or poorly supported.
Gears 5 - See above
Halo: The Master Chief Collection - See above
Halo 5: Guardians - 84
Forza Horizon 3 - See above
Forza Horizon 4 - See above
Forza Motorsport 6 - See above
Forza Motorsport 7 - See above
Quatum Break - Single player
Killer Instinct - Maybe you can count this as a MP focused title but Shadow Lab and Shadow Lords are incredible content for SP gamers. Either way, like Gears, this is a game with strong MP elements but it certainly doesn't fit any of your criteria. It reviewed well and got great support post launch
Sunset Overdrive - Has co-op but this was not a MP focused title
Bleeding edge - Literally just came out and we know more content is coming
Crackdown 3 - Not a MP focused title and has seen multiple updates for the campaign mode
Recore - Single player
State of decay 2 - Has co-op but is not a MP focused title. Has seen great support post launch and a majority of that support is for the campaign mode, not MP
Sea of theives - One of the few actual MP focused titles on this list
Super Lucky's Tale - Single player
Zoo Tycoon: ultimate Animal collection - SP game with a co-op option added years after release
Rush: A disney/pixar adventure - Has a split screen/couch co-op mode but is not MP focused
Disneyland Adventures - Another SP kids game with optional local co-op
Phantom Dust - this is a MP title but is a port from OG Xbox
Voodoo Vince: Remastered - Single player
Halo Wars 2 - Has MP but is not MP focused
Dead Rising 3 - I changed this to DR3 because DR4 was just a timed exclusive. DR3 is another SP title with optional co-op
Project Spark - Has MP, but I wouldn't say this is MP focused just like I wouldn't say Dreams is MP focused, its focus was whatever game you made
So going by your own list there doesn't seem to be any over-emphasis on multiplayer titles and the titles with strong MP focus mostly got real good reviews and support.