A lot of Americans are the result of cousins marrying cousins - including me.
The original settlers of the colonies, especially the upper classes, brought over the old customs, and many of the gentry married their cousins.
My family never left Virginia, from the 1600s to the early 20th century. A lot of them married cousins, for class and wealth reasons. I have a Virginia cousin who married another Virginian in the late 1960s, and learned many years later that the two were distant cousins.
I’m not advocating it - the royal houses of Europe definitely became too inbred; but I recall reading that even the folks on Pitcairn Island didn’t show that much damage from inbreeding. They had a lot of tooth decay, but that was probably from all the sugars in their available staple foods, and poor dental hygiene.
Just another metrosexual.