Well... let's say you're a politician wanting to regulate Facebook, and let's say you have an affair with whom you communicate on Facebook or in Instagram DMs. If I were Facebook, I'd simply let an investigation team check if any dirt can be mined out of the troves of data - anything, even the dataset of GPS or other location pinpoints, can be enough to get a first hint. And now I discretely contact you and advise that there may be information around and that it would be a pity if that information were to get public.
This is the ultimate problem with the size and capabilities that companies such as Facebook have.