Why was it that in ancient times it was all about the extended family Why did the family get smaller the more the times progressed and now it's hard to see extended families with three and four genera

Why was it that in ancient times it was all about the extended family Why did the family get smaller the more the times progressed and now it's hard to see extended families with three and four generations together? It's hard to keep track of everyone, that's the reality. In ancient times, the big family was because of cultural traditions and the cohesion brought about by the authority of the head of the family. It's not that small families don't have conflicts with each other and don't want to develop independently. Modern people are pursuing a stronger and stronger sense of independence, and there is no longer the original cultural and institutional soil, the big head of the original authority, naturally, it is difficult to reproduce the history of several generations of the same family.