>Given it just needs to be done once

Since it is still the early days I think they are hesitant to ban every insecure device once one is discovered. This greatly decreased the cost for attackers.

>and a hdcp stripping device

Those only work with older versions of HDCP. Over time newer versions of HDCP will keep making the security better making it eventually impossible for an external splitter to work. No such splitter exists for HDCP 2.3 which came out 6 years ago.