We're in the context of Boost here and it has great support for Windows. Switching to a build system that doesn't have mature support for Windows is simply a non-starter for the Boost project.
That a lot of FOSS projects (understandably) have poor support for Windows doesn't mean that all of them do. It also doesn't mean there isn't demand for FOSS projects on that platform.
That a lot of FOSS projects (understandably) have poor support for Windows doesn't mean that all of them do. It also doesn't mean there isn't demand for FOSS projects on that platform.