COD is a big deal but let's not overstate things, only about 12% of PS4 owners play COD so while not totally insignificant it's far from the only thing people play on PlayStation. Yes they get money from microtransactions and game sales but it would be a terrible business move on Microsoft's part to make COD exclusive to one platform. They could use PlayStation players to partially subsidize gamepass on xbox. Once this deal is done when you add Activision/Blizzard employees to what was picked up with Bethesda the overall headcount at MS will be up by 10% that's a lot more paychecks going out and benefits paid monthly than they had in 2020. I have a series x but also haven't purchased a COD game in years and don't really plan to so there is no skin off of my back one way or the other.
Gamepass was already not making any money and that was before they spent nearly $80 billion picking up two publishers. If I were Spencer I'd make sure COD stayed multiplatform and brought in as much cash as I could from it, it's likely most people who paly COD on xbox are already GP subs so there is a limit to how many people are going to sign up for that service and there is no way they bring every COD player over from PlayStation, a decent number of people will just do without the game if it goes exclusive so let Sony fans pay full price, bring in tons of cash from them and let people in your ecosystem pay monthly, everybody wins.