Microsoft started the Windows transition to git sometime before Github acquisition as a part of a company-wide effort to move to VSTS/Azure DevOps Repos internal dogfooding. The choice there was between the zombie ghost of TFS source control or git, so you can possibly imagine some of the reasons why they chose to put a lot of time/effort into making git work for themselves. The subsequent acquisition of Github seems to have made them even happier at the switch to git.
