IIRC "quality approved necessary documents" are also exempt from discovery in malpractice cases, so there's no risk to holding onto them.

I dont think that is accurate at all. Lawsuits often turn on quality docs specifically. A simple example would be be something like a memo that states a defective product can still be released to market that goes on to kill someone. Another example would be a quality approved design document that shows infringement on competitor IP.

Most quality docs must be retained by law for the life of the company, even if they discontinue a product. So it isn't really judgement call from the legal department.