The problem with the old Whonix Windows installer was that it required an actual Windows to build the Whonix Windows Starter as well as the Whonix Windows Installer. Therefore it required a contributor to keep building the WIndows installer. A manual, repetitive, laborious, tedious process. The contributor is no longer active. Hence the Whonix Windows Installer was deprecated.
The new wixl based Whonix Windows Installer can be cross build from Linux for Windows. Build dependencies are available from packages.debian.org. Therefore it can be automated, integrated into the Whonix build process. Then maintenance should be much easier. Cross building documentation isn’t available yet and integration into Whonix build process (derivative-maker) is still open TODO.