I believe people think you put pictures on FB to get that kind of compliment. My friend puts her pic and her daughter's pics on there with that airbrush app or whatever it's called, and they have porcelain skin and huge blue eyes (both their eyes are pale blue), and everyone gushes how gorgeous they are. Don't they see it's a fake picture? Of course, they do, but as you say, it's an insincere comment. Even if you post a picture with cat whiskers and ears, "OH, you are BEAUTIFUL, SO STUNNING." It's what they think you expect, and it's shallow as hell. Good observation you wrote about. I think the same way.