The comment was about importance, not popularity. Those aren't mainly used for important work. If people are paying you to use the software, it's probably important to them.
Tablets, smartphones and smart tvs have been of increasing importance on education activities, specially after the pandemic. My router is used for ALL my internet traffic, important or not. Webservers... basically most of what most things people do online. And supercomputers are right now doing high relevancy tasks like running climate models, simulating protein folding, drug interactions and improving vehicle's safety.
I'd disagree those aren't mainly used for important work.
That very same kernel runs on the majority of smartphones, tablets, smart tvs, servers, routers and 100% of the biggest super computers out there. This very same kernel literally flies on Mars. Although my sample size is small it is not biased neither are the referred market segments.
And while Mars and supercomputers are cool and important for society and humanity in general, there is also no denying of the immediate impact that Windows has in most human-interfacing applications.
Supermarket checkouts, public services, small-scale logistics, health, just plain old office workers, and so on.
An undeniably large slice of companies and public sectors that do not have a dedicated IT staff rely on Windows-based computers to organize and operate their activities. Outages to those probably have more direct impact on actual everyday people going about their lives than an outage in a Mars rover or lack of WiFi access.
Just to be clear I'm not playing teams here, *nix-based systems are ridiculously important too, but the open-source base is arguably a more - democratic? healthy? stable? I lack of a better word - development process, and its importance does not lessen the importance of other systems.