That is an interesting point. I remember spending a fair bit of time 10 years ago looking up LCD monitors which did not have any kind of HDCP hardware, and bemoaning the fact that any graphics card faster than a Geforce 7900 did (and this is one reason why I’ve still got 4 of them in a box somewhere).
However, there is a flipside to this. While HDCP has been broken quite some time ago, it is still an encryption scheme. The purpose of any encryption scheme is to remove all useful patterns in data - to make it look like noise. For a set power level, noise does not travel as far as a well-defined signal - meaning that an HDCP link provides some resistance against Tempest attacks.