Is this why Americans, as a whole, are considered more attractive?

As a non-American, I've noticed that many Americans who can afford it are very concerned about their looks, consuming a variety of beauty-enhancing products so I think this is definitely a factor. But I've also noticed that in terms of facial symmetry- the kind of stuff you are born with- Americans are what you would call "attractive." I think this has much to do with racial/ethnic diversity. In most other nations, groups are endogamous whereas in America, the various ethnic groups of Europe and later, of Asia and Africa intermixed. Biology tells us that generally, the more genetically different your parents are, the healthier you will probably be. Do you think this applies to beauty as well?