Because they want people to buy Xbox rather than PS. Sacrificing some short term revenue while you buy up the all the large franchises and lock them to your console serves that purpose quite well.
Game Pass and Xbox Cloud are their big push at the moment. If those are where they see the future of gaming going then it doesn't really matter to them whether someone buys Xbox or not. It only matters that they have a device that can play Game Pass games or can run Xbox Cloud.
Currently this means that they don't care if people have an Xbox or a PC. Xbox is there for people that either cannot afford a PC or prefer console gaming. PC is there for people that don't want to game on console and can afford a PC.
Same reason they don't mind having their games on Steam. Sure they "lose" 30% from each sale, but they are gaining 70% of that sale where if the game weren't on Steam, they would "lose" 0% but they'd also "gain" 0% additional revenue from a sale on Steam that wouldn't be happening on either Xbox or the MS store.
MS are either thinking very very long term or there is a ROI factor here that we're not considering. Anyone have a grand total now for new studio/publisher investments since GamePass was launched?
How about this. MS uses COD as leverage to get Sony to allow Xbox Cloud on PlayStation consoles. Maybe even try to get Game Pass on PlayStation consoles. That last is obviously unlikey, but then who would have predicted MS buying Activision-Blizzard.
COD makes Sony a lot of money. Would Sony be willing to allow Xbox Cloud on PlayStation consoles if it meant that it would guarantee that MS continues to release COD on PlayStation consoles?
On the flip side, having COD on PlayStation doesn't really hurt MS as they'll still be bringing in 100's of millions of USD (possibly billions) a year via sales of COD on PlayStation consoles.
Doing so also allows them to potentially avoid some major negative gamer backlash and negative publicity. And if they can get Xbox Cloud on PlayStation consoles, that would be a win for them.
Regards,
SB