IMO, at the time, it was to buy ABK and make CoD an Xbox exclusive. That clearly didn't play out when everyone screamed about it being (rightly!) anticompetitive, and so they had to resign themselves to accepting that day 1 gamepass exclusive was going to be their way to get people to switch over from PS. That also didn't work.
The 'K' part of ABK was also probably going to be their way to drive mobile into Xbox as well with their 'everything is an Xbox' push at the time.
This is not even considering they basically bought all the PR issues that came with Blizzard.
Instead, they paid way over the odds for IPs that seem past their prime.
Another crazy deal like this is the EA's buyout, I wonder if it will come through or the investors will eventually realize that they are not going to see their money ever again.