Right. Windows support is a feature outside of the scope of Linux package managers. If they weren't tethered to specific distros I don't see why one couldn't support multiple platforms. It hasn't historically, but Windows has a bunch of package managers, even one supported by Microsoft.
I think "largest" is quite an exaggeration since historically scripting languages packaging has been rather terrible on Windows. While Windows was a consideration for languages like Python (I've read they avoided Make because of Windows), for me cygwin always coming up along with it until recently.
I argue that's simply not true. Scripting languages came up with package managers because the largest platform (Windows) does not have a package manager. Actually that scripting languages implement package managers is a very good argument that their functionality is desired. As a side note, every language package manager is much worse in my experience than all of the system package managers I ever used.