Think of it like so: you have a robot that anybody can ask anything and that will answer any and all questions truthfully. Whose fault is it if you deliberately tell the robot non-public information?
Why the content receiver? That would be like a musician suing viewers for listening to their copyrighted music playing in the background of Youtube videos. It's the responsibility of people disseminating content to ensure they have the right to do so. That's why file sharing cases focus on the sharing, not the downloading per se.
