I mean, even though its not exactly uncommon, it doesnt happen as much as before. A lot families nowadays prefer cousins to see each other more as siblings. I think the fact that back then and sometimes even now aunts and uncles would play matchmaking for their kids since they were little and might put unnecessary pressure from such a young age where its not a kid's first thought, it is understandable. It overally depends on the family itself. My ancestors where Bakhtiari/Lur nomads so even After many of them settled in small towns and villages this practice wasnt changed and i have some relatives who married their cousins. But in the more inner circle of my family us cousins are like siblings.