https://www.worldatlas.com/articles/...in-the-us.html
Because it has the greatest cities and national parks in the world, that's why. No other country comes even close.
1. New York, New York - 59.7 million visitors
2. Chicago, Illinois - 54.1 million visitors
3. Atlanta, Georgia - 51 million visitors
4. Anaheim/Orange County, California - 48.2 million
5. Orlando, Florida - 48 million visitors
6. Los Angeles, California - 47.3 million visitors
7. Las Vegas - 42.9 million visitors
8. Philadelphia, Pennsylvania - 42 million visitors
9. San Diego, California - 34.9 million visitors
10. San Francisco, California - 25 million visitors