Having a preference for any human be it a man or a woman to be is strictly an individual choice and people chose their partners in a relationship based on their personal choices which might be a normal thing or just superficial. I don't know the statistics of American men that goes for foreign if it really in the increase. But from observation I think generally men going for foreign wifes or women could just be about the specs of those women. Maybe they might like their physical body's structure, like them being sexy, glamourous and elegance. Some may just be about wanting a woman from a particular country, maybe the man is having the intention of moving that way some day. There can be diverse interest which can prompt them to go for foreign women.