Not everybody uses linux out of conviction, idealism, or principle. Many use it either by chance or convenience. The purists are probably not the majority of linux users.
There are people who already won’t switch to linux because windows has WSL. Gaming has held back many people from switching too, although that’s becoming less of a problem. However, if there were no reason to switch to other distros, and an M$ distro were to become the most used distro…
Do you know what M$ did when they had the largest market share for browsers? Do you know what Google is currently doing with their marketshare on the browser market?
Windows has a pitiful representation on the server side, but if that changed to an M$ distro with proprietary linux modules in order to make certain software work (or something more insidious that I can’t think of), it would change the server landscape too. And suddenly, you can’t write stuff for the most popular servers without installing M$ kernel modules or software.
The linux zealots are not the majority. Zealots never are.