Here are two real-world (not hypothetical; a (self-employed) person I know actually has these) problems:

* The person needs to exchange forms in Word Documents with other people (agencies and public authorities) on a daily basis, and the exact formatting matters, so LibreOffice doesn't cut it.

* There is trade specific software for which there is no alternative (open source or paid), which the person couldn't replace with an alternative if there was one (because it's effectively agency mandated), and which only runs on Windows. (And to give you a sense of how special-purpose this is: it has it's own hardware VPN box which you have to put between your computer and the internet.)

So it's sad, but the requirement is not "at least as good as Windows" but "Windows".