Please forgive my stupidity, but is there any particular reason why companies never seem to disclose what "system" of theirs was breached? If this breach came about as a result of a security incident at a third-party, would it not benefit everyone minus the vendor to shift the blame? I understand that they say "our systems", but I've seen companies say this before when what they mean is "a system controlled by a vendor we contracted".

My understanding is that companies tend do disclose the bare minimum they are required by law, and keep everything else to themselves.