Launching all your major exclusives and paying for Game Pass deals for other titles will net players (I know it got me) but like eventually you're going to reach that peak of players.
Couple that with the issue of Microsoft game output slowing down a great deal to the point that they're just not releasing as many high quality AAA games at a pace that fuels the Game-Pass model, nor are they able to keep throwing money at other studios for Game Pass releases of third party titles.
Call of Duty is a band-aid as it will no doubt get people in and keep them engaged (people play CoD all year round), but they're no longer in the running against PlayStation and they're games are not exclusive anymore. They seem to be coming to PlayStation eventually, so why as a PlayStation player would you consider getting a PC or Xbox for Game Pass?
It feels like the model is great for consumers in terms of offering a massive library of games you can access, but it is terrible for Microsoft who basically need to keep it stocked with licenses and keep getting licenses to keep you coming back.