Why does Iraq prefer that the woman remain in the clan by marrying the son of her father’s brother, rather than marrying a cousin in a different clan? In other words, is the purpose of cousin marriage...

Why does Iraq prefer that the woman remain in the clan by marrying the son of her father’s brother, rather than marrying a cousin in a different clan? In other words, is the purpose of cousin marriage simply to ensure that children find a suitable spouse or is there more involved in the choice than that?