In addition: if other people are working on the code base, I find it very insightful to first read what task/issue they are working on and then look at the commit they made. I then try to see if I understand why the commit implements the described task or solves the issue.
You can do the same if nobody is actively working on the code but you have the history in source control.
TFS has first-class support for Git repositories (in addition to the classic TFSVC repositories). So yes, they're moving more and more to Git. But no, they're not abandoning TFS.
Interestingly, however, most of their "open source" efforts (.NET, C#, and related) are all on GitHub rather than their own hosted offerings: CodePlex (which is basically dead) or "Visual Studio Team Services".
Not sure why Visual Studio Team Services is in scare quotes -- that's the product's name. And it's not an open source hosting service, which handily explains why Microsoft's open source isn't hosted there.
Disclosure: I'm a PM on VSTS/TFS, and I own part of version control.
Are those scare quotes or just regular old quotes? TFS and associated technologies have been through a lot of names (Visual Studio Team System, TFS, Team Services, and probably a few I can't remember).
Microsoft is moving to Git and we use Team Services / TFS as our Git server for all private repositories. GitHub is only used for OSS since that's where the OSS community is.
It's also not just the community, but GitHub provides significantly better integration support, than GitLab. Since GitHub has such a robust API, it's easier to create bots and what not, to help better manage large open source projects.
Reading release notes of TFS, they seem to be putting much more effort into improving integration with Git compared with TFVC. This may be just to catch up to acheive parity with TFVC in TFS, but it was enough for me to abandon TFVC for Git in all new projects.
You can do the same if nobody is actively working on the code but you have the history in source control.