It's not easy for foreign people to adapt to new customs and follow another culture.
Some people have in their cultures big differences in their behaviors.
These behaviors sometimes can be shocking for other people from a different culture. In my case, I have never had any difficulty because our culture in Colombia is pretty similar to the US culture. I don't mean that we have the same customs, but at least we can understand why American people have certain manners and ways of behaving. When I analyze and think about people from other countries or continents, I can conclude that it's harder for them to understand and follow new customs because of the huge difference between their culture and American culture. Because of these big differences, some foreign people, especially people from Asia and Africa, prefer to keep their own customs.