I think the Xbox version of Activision games may have more exclusive content like extra levels or characters to convince people to buy a Xbox Series X.
I feel like most Activision games are at lower price points to begin with, at least on Switch, so even if that's the case, I always expect decent sales.
I think it's about Microsoft positioning themselves to get out of the console market and move forward more as a publisher for PC and other consoles. If makes sense for them, the Xbox has effectively just become a PC anyway, so if they focus on Xbox-as-a-service and publish games to other platforms they're still pumping out their products, but doing it without the overhead of hardware management, just like with Windows.
Call of Duty on Game Pass is going to get me to buy into Game Pass as it pays for a 1/3 of the cost or I think a half if you get the console only one. So, now it has gone from a meh list to a much better list as it includes a yearly release that costs me $70 anyway.