Unfortunately, there are too few hardware developers and not enough hardware-awareness, thanks to the good abstraction nowadays. In the modern age, only few software devs cares about the underlying hardware, because it just works. The thing is, software _runs_ on hardware and any bug/backdoor etc in it undermines everything above.

Did you know that the baseband chip in your smartphone runs it's own linux? Or that every SIM card comes with java applications that can communicate with it? I guess not.

Considering how much hardware is required on a modern PC main board, it's really not that surprising that there are backdoors, bugs, or other mechanisms that can be exploited.