I think there may be an element of survivorship bias at play. There's kind of a 2x2 you can draw where people can be publicly/privately kind/abusive. People who are kind all the time (or at least, not abusive all the time) are unremarkable, I'm not sure there are many people who are publicly abusive and privately kind, and people who are both publicly and privately abusive are way more likely to end up in prison, or homeless, or otherwise away from people. So that leaves us noticing the strange pattern of people who are publicly kind and privately abusive. It's like, the most remarkable pattern that's actually present for us to remark upon.