DRM and Content contracts. They can't just throw 4k into an unsecured environment because they need to make a best effort to enforce that their 4k content isn't pirated.
And Netflix exclusives regularly make it to pirate sites in 4K afaik?
Yes, generally the day of release.
No 4K versions of most shows from the last month.
This is why you can't screenshot Netflix on Windows/Apple - the region where the video is will be black.
Not disagreeing with you, just pointing out their faulty reasoning.