>There is completely no need to prevent users from retaining a copy once they watched it.
For Netflix there's one big reason to: PROFIT
For Netflix there's one big reason to: PROFIT
The profit that comes from actually having content to offer, which wouldn't happen if they didn't have DRM to "protect" the studios' shows and films.
Regardless of their opinions on DRM, it's not their decision to make, unless they just want to stream self-produced content.
Of course it wouldn't have the same scale. But we aren't talking about scale - you mentioned existence as if selling something DRM-free is not possible or not sustainable.