Well, there are an infinite number of lifestyles to be lived. I doubt there are good numbers on dormitory-style lifestyles, for instance. But current numbers show that married households fare well.
Married households fare well because the tax system and plenty of other institutions favor married households. It doesn't have to the the case.
Marriage is mostly a "capital" redistribution system and with strong public services (ie shared services) there is much less need to focus on the nuclear family as a protection (sharing of ressources) network.
Ex. When a few years back pension laws changed in Japan and housewives got the right to get a pension separately from their husband, the rate of divorce boomed.
There is nothing in the nuclear family that makes in a natural fit to what humans are as social animals.
Marriage is mostly a "capital" redistribution system and with strong public services (ie shared services) there is much less need to focus on the nuclear family as a protection (sharing of ressources) network.
Ex. When a few years back pension laws changed in Japan and housewives got the right to get a pension separately from their husband, the rate of divorce boomed.
There is nothing in the nuclear family that makes in a natural fit to what humans are as social animals.