If it makes you feel any better, comparable tools either take the same “different OS different license” approach (iA Writer) or have a subscription model (Ulysses). 
Yeah, unfortunately the iCloud app on Windows doesn’t seem to work very well with Scrivener. Here’s a recent thread from a poster who was also trying to add a PC to a Mac workflow, who encountered similar issues with how poorly iCloud runs on Windows.
The method suggested by Kewms of transferring zip backups back and forth between machines will work. You might also consider giving Dropbox a try for syncing your live projects. The Dropbox app works relatively flawlessly on Windows, but I have no idea how well it performs on the Mac side. (Mac posters here seem to either love Dropbox or hate it.)
Best,
Jim