Not that uncommon among Muslims-Saadam Hussein married his first cousin.
An infidel, Rudy Giuliani married his second cousin. -Tom
The dowry and chaperoning rules almost push people that way.
Marry a paternal first cousin, and there’s rarely a dowry. Two brothers swap sisters, and there is no dowry. Free brides for everyone.
There is some protection for the woman when they marry a male cousin. She probably remains in the same family compound as her father and mother, so she has more family to protect her than if she marries a stranger. She also has more potential chaperones like brothers and her father if her husband won’t take her out.
The chaperoning system means she has to be out with a man who is related. The cousin is the only man that can both chaperone and marry her. That’s the only man she can “date”. It leads to more marriages.
What makes things so much worse is that the patrilineal marriages pretty much have to repeat to keep the benefits. So it isn’t one generation of cousins marrying - it may be several where there is rarely a new addition to the gene pool.