I do not think there are mysterious cases. There are just some where people chose not to cooperate enough for us to make a determination and that is their right.
Well. we learn over time. Before Herbert Needleman, the dangers of lead poisoning were known, but it's effects upon people, who from childhood were exposed, and they ended up being violent criminals - that was fairly new, and compelling enough to knock some sense into people.
Another case I know personally, a friend had adopted a young boy, who was troubled, and the thought was a better environment would eliminate those issues. I liked the kid. Most of the time, he was great. Outgoing, friendly, smart. But he was still getting into trouble. I noticed that it was three months behaving, then a short period of bad. I mentioned it, but everyone thought that was 100 percent coincidence. Eventually they figured out I was right, by that time, he'd committed some serious crimes.
Some sort of chemical imbalance? That was my guess. Point is, yeah, we're going to find out more reasons as time goes on. The question is what makes the people in your example not cooperate?
Also note that there are quite a few "too important to jail" cases, see, for example some prominent stock scammers or rapists and child abusers or murderers/war criminals. These cases are probably the worst, because they give not-smart people the impression that you can get away with it. And hence overall ethics decline.
People should not ever decide that since "the man" got away with something, so it is perfectly alright to do the same things. If that is the case, they deserve the punishment, even if "the man" is not. That. is the most masochistic example to whataboutism on their part.