Meager amounts of solidarity are quite normal: after all, the way the world is set up, lots of games are zero-sum or mixed-motive. People have hence conflicting interests. This is not a fertile breeding ground for solidarity.
In-group solidarity appears when there is a threat, real or merely perceived, to the group as a whole. When zombies attack your house, it doesn't make much sense to bicker over who'll have to do the dishes once it's over.
This kind of behaviour is quite rational. By that I don't mean that the solidarity that flames up spontaneously in groups of humans when an external threat appears is the result of cold-hearted cost-benefit calculations. Rather, I think we're predisposed by nature to act like that, because throughout evolutionary history, this way of behaving maximized inclusive fitness. It's nature's way of concentrating the mind on the essentials.
Perhaps people who long for the warm glow of solidarity should instead be thankful that they live in a society that is not subject to a serious external threat. If you look at human history, it turns out such a state is rather rare.