In the Symantec case, the private key in question remained with Symantec at all times, with employees who legitimately had access to the EV certificate authority as part of their job, in the course of testing. It was never exposed to anyone outside the CA.
CNNIC sold a valid, unconstrained intermediate private key to a completely unqualified customer and had organizational troubles at all levels. We were lucky that the customer was also incompetent, and just got caught. Symantec had a few employees make a mistake internally, and at no point could anyone malicious (other than potential malicious employees) threaten internet security. And those specific employees got fired.
Link to this? The story was that they issued it to some v Egyptian company that wanted to run a CA. This company was incompetent and didn't have an HSM. They did have a Palo Alto MITM box that had "CA capabilities", so they used that. Then an engineer at this company plugged his machine into the MITM port, loaded Chrome and tada.
Utterly incompetent and against the CA rules. But not large scale or non-consenual MITM right?
Putting it in an HSM does not make it OK.