Microsoft licensing goes way beyond Windows - there‘s the whole range of office software (which you can also license on Mac), then all the server software, etc.

Microsoft licensing goes way beyond Windows - there‘s the whole range of office software (which you can also license on Mac), then all the server software, etc., most of which should does not apply to Gitlab (unless they want to deploy on linux and switch to SQL Server as database, but I doubt that). And then, if you‘re big enough, you can negotiate corporate licensing to save money, which requires license management etc. I doubt any of this applies to Gitlab as they stand.