Every situation has its pros and cons. The joint vs nuclear family debate is no different and has been around for a long time.
The world and peoples values have evolved. A nuclear family is about self interestt and teh maintenace of the interests of the closest family. The joint family is about caring for a broader community.
In days gone by the joint family was the place where there was security from outside enemies. The larger the numbers the greater the protection afforded its members. This system worked well when there was greater attachment to social structures like the extended family, clan, tribe etc.
With the rise in nation states, this system became less needed and the nuclear family began to rise in importance. In the current materialistically orientated world, the nuclear family has taken the place of the joint family as each tries to secure enough resources for themselves and their chosen few.
Coming to Punar Vivah, the joint family still functions because of the strong patriarchal system that operates supported by a strong matriach. Joint families do not flourish where all the members have equal authority.
More and more people are bringing demanding a greater say in their own lives and thus the joint family which is based on patriarchy does not survive.
The nuclear family however, in giving people the opportunity to make their own decisions also robs them of the opportunity of communal wisdom and sharing of problems. The high rates of divorce and visits to psychiatrists are testimony to the fact that there are no longer sufficient support available in the nuclear family.