I believe these piracy groups arent hijacking the HDMI signal. They're cracking the Widevine DRM chain to grab the audio and video data from the stream and repackage it into an mkv file.
In 2010, an HDCP master key was leaked, allowing anyone to generate an infinite number of valid new HDCP devices. This has made HDCP useless for stopping piracy for the past 15 years. All it's done since then is add another point of failure between people's electronics and their displays.
Wonder how many people lost the ability to play ~~their content~~ the content they were licensing when they released that update, and had to buy new hardware because it was no longer supported.
