It's actually an interesting point that I have given some thought about in the past.
If you read Shadows of Our Forgotten Ancestors, by Carl Sagan, you will find that chimps are "racist" and organize themselves into tribes which would be somewhat inbred, were it not for the occasional contact with other tribes, which freshens up the gene pool.
As I'm sure you've noticed, some people are really attracted to "exotic" types, say, blonde, black, foreigners of any kind, and indeed in my family tree there's occasionally some guy from a neighboring village.
And, of course, you need to take into account that the average distance between villages is about an hour's walk around here.
Each town has a special patron saint, and holds a yearly party on that date, which tends to attract people from other small towns, given the limited options they have for entertainment. It will generally involve an amateur, simplified form of bullfighting, barbecue, wine, fireworks, bell tolls, and maybe some amateur band, though many places have their own small orchestra.
I have no doubt there's plenty of young people rolling in the proverbial hay afterwards