I see this kind of alleged puzzlement a lot here and on the internet in general. I'm not puzzled by it though, I think it's usually insincere and simply used as a cheap rhetorical device to dismiss people's feelings and reactions without actually making an argument.
For the very few people who genuinely don't understand: this is part of the human condition. People aren't "rational" according to a text book. People's happiness and feelings depend hugely on contrasting situations. Whether it is your situation now compared to your situation before, or your situation compared to your neighbor's situation. In many cases this has a bigger impact than the "absolute" situation. And the misunderstanding or disregarding of other people's feelings does not invalidate them.