When you think about the implications of farming vs. nomadic hunting/gathering it may be a logical outcome.
Farming means families are going to stay in one place together, probably for most of their lives. Not much choice of finding a mate from outside the immediate family group/clan/tribe.
Nomadic hunting groups however might well run into other families with the ensuing wider choice of mates.
That’s less of a problem — the main problem is lower infant mortality leading to large family sizes; in my own tree a few generations back, one of three brothers who settled near here married into another large family; he had a niece who married one of his wife’s nephews, and from his other brother a nephew who married one of his wife’s nieces. At that time, given the lower overall population and sectarian isolations, it pretty much had to happen that way.