Microsoft is a heavy user of git internally (e.g. Windows is now developed in a git repo) and though they do also have their own source control as part of VSTS

Microsoft is a heavy user of git internally (e.g. Windows is now developed in a git repo) and though they do also have their own source control as part of VSTS they've also had first class support for git there for a while too so it isn't really that surprising.