Sure but almost no OSS projects build containers for Windows (to my knowledge). The same goes for XNU/darwin afaik. They may get binaries but container images often assume Linux by default.
Developers, ime, also don't really want to start building their own container images for auxiliary services like, e.g., PostgreSQL, MongoDB or MySQL.
Having virtualized Linux support means you can take the existing ecosystem and make it accessible to the other two.
It also means docker itself doesn't have to fully embrace & support either which is part of why it's "cheaper".
Developers, ime, also don't really want to start building their own container images for auxiliary services like, e.g., PostgreSQL, MongoDB or MySQL.
Having virtualized Linux support means you can take the existing ecosystem and make it accessible to the other two. It also means docker itself doesn't have to fully embrace & support either which is part of why it's "cheaper".