Look at it from Netflix’s perspective: most of their collection has legal strings attached, even most of their exclusives, with substantial penalties if they don’t take measures to encumber content and there’s a real threat of auditors catching implementation lapses. If they use HTML video with EME and someone comes up with a way to copy it, that’s a problem for Google’s Widevine (used by both Chrome and Firefox), Microsoft, Apple, etc. as long as they can show they used the system correctly. Similarly, they don’t need to be absolutely perfect in region locking as long as they can defend the mechanism in court. Similarly, VPN detection needs to be at the level where they have a good chance of avoiding a court case – auditors definitely know to try that.

Now ask how many Linux users running Firefox without the Widevine CDM installed over a VPN there are likely to be and how much revenue that brings in compared to the legal risks of not being able to check those boxes.