Muslims marry their first cousins for the same reason they marry pre teen girls. Mohammed did it, so it is more than OK. They do it by choice, not because of geography.
Dowry practices have a lot to do with it. You have to pay for a bride unless she’s taken in conquest.
Marry a paternal first cousin, and the dowry is grandpa folding his money over and putting it back in his pocket.
Two cousins marrying each other’s sisters means no one has to pay dowry.
And if she marries her paternal cousin, she has a lot of benefits under Shariah law:
* she doesn’t have to veil in front of her father in law or brothers in law
* the father in law is an uncle and thus can escort her and the kids to events when the husband is gone or even refuses
* she probably lives in the same compound with her own parents and siblings and thus some protection because her kin are around her
* if you marry your paternal cousin, there’s a fair chance your brother is still around to offer protection, act as an escort and act as your representative
* if she is divorced, she simply moves back into her parents’ rooms but isn’t sent miles away from the kids, and if the father dies and the kids go to his brothers to raise, they are likely still in the same village