In those two cases they also use VMs because they don't really have another cheap option.
Neither XNU/Darwin nor Windows have had an oob option for running Linux images. WSL is rather new in comparison.
Neither XNU/Darwin nor Windows have had an oob option for running Linux images. WSL is rather new in comparison.
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".