[sbx320]

Screen captures aren't too common since they would incur an additional re-encoding step (losing a minor bit of fidelity), so for the more "professional" rippers it isn't a proper option. Instead they use the raw data stream from the streaming platform, strip the DRM and reassemble the video file. Of course the DRM stripping is the hard part with not much public knowledge being available.

As you mentioned, the quality of those rips is a bit worse than a blu-ray rip, but if the blu-ray isn't available there's not much you can do. People will just enjoy a slightly worse quality version (just like they did with shaky cam rips).