To be fair, it has been the dominant mode of familial organization in colonial powers for the past 100+ years. When economics are stable from generation to generation there would be far less tendency to split households - only in times of abundance or want would it make sense for each generational unit to live separately. Killing off natives and taking their land and resources tends to create an awful lot of abundance. The nuclear family thus symbolizes prosperity and the right-wing mythological ideal of past abundance that can be regained by returning to "traditional values".

Multigenerational families are hard to move, and come with a lot of baggage (hah).

That gets in the way of Empire and economic flexibility.

>To be fair, it has been the dominant mode of familial organization in colonial powers for the past 100+ years

Has it? I thought most colonies relied on corporate families.

The colonized often do - the colonizers are the ones splitting and creating new families as quickly as possible in order to occupy more resources and grab a larger slice of the opportunities afforded by empire.

Perhaps but when I look into examples of corporate families they are almost always in a colonial context. Like you might be more likely to fragment if opportunities exist, and franchise out. But you still get the same stories of a family farm or workshop being owned and operated by multiple generations until the young ones get a tertiary opportunity to take on something else.