This leads to the question of why this might be so; how might nonsangunity confer a survival advantage in a given time and place?
We could speculate that, in a mileu of widespread territorial warfare, NST might have an edge in overt combat.
However this would seem to apply only to A types, there being little conceivable advantage that PA types would have in that dimension against NA and NPA+ types, and the first NST might have been PA rather than A types anyway.
So more likely in my view is this:
We know that the N trait confers sociability and that nonsanguine types are in general innately lower in sociability than sanguine types. On a collective basis lower innate sociability might manifest itself in a lack of warm feelings toward outsiders, in formal terms a lack of out-group altruism, with another corrolary being a higher degree of negative ethnocentrism, that is, hostility toward outsiders. So I would surmise that in a mileu where these qualities were particularly beneficial to outcompeting other groups, the proliferation of NST would be highly advantageous to group survival.
It was noted that the Bedouin were primarily NA types, in contrast to other areas of the Middle-east. And the Sanguine Bedouin are renowned for being highly hospitable to outsiders. Which might account for their nomadism and lack of clearly delineated territory compared to other Middle-eastern groups?