According to The Verge senior editor Tom Warren, as early as July this year, the British CMA approved Microsoft's acquisition of Activision Blizzard. The reason why it was not announced until now is to find a suitable company to sell cloud gaming copyrights.
Tom Warren said that many companies were vying for Activision Blizzard's cloud gaming rights. The CMA provided a list to Microsoft, and Microsoft finally chose Ubisoft.
July of this year was also the date when the US FTC lost its lawsuit against Microsoft. At that time, it meant that Microsoft's acquisition of Activision Blizzard was no longer an obstacle in the US, and the only obstacle to the acquisition was the British CMA, which rejected Microsoft's acquisition of Activision Blizzard in April this year.