The CMA is an independent body, that's the point of it. The Government is currently Tory and they love money and big business so would pass this though in an instant if it was up to them, and would probably try to make bank of it if they could.
I don't agree with the CMAs decisions on this matter, but there's a good reason MS are going to such lengths to keep them happy in the long run.
At the end of the day, it's not like Gamepass is so bereft of releases this year we desperately need the Acti-Blizz catalogue, we can wait.