When I wad in Dublin (and surrounding areas) for St Patrick's day, or in Munich for Oktoberfest, or any of the other cultural centers for a holiday && they had the same types of shenannigans as the US going on ... were they mocking us mocking them?
That could get confusing.
In truth, immigration in the US change both cultures. Sometimes it is fast, sometimes it happens slowly. In the great American experiment that's part of the point. Where do you think the melting pot analogy comes from? It's an exchange and mix of many traditions and ideals adopted in varying degrees, by varying subcultures, across a great land mass. Only because of the ease of travel, and modern communication systems are we so keenly aware of it happening.
Why do you think that, unlike many other nations, we don't have a language requirement for immigrants to become citizens? We swear alligence to the US, and not to our individual state of residence, etc. etc.
The very roots of our nation are built on controlled change in such a way that there is a single US identity made up of a mix of continuously evolving cultures. We are not a nation of conformists, and static cultural norms. We are a nation of rebels, of radicals, and freedoms thad drive us towards constant progess, and of change.
Sometimes the change is good. Sometimes not. We will find a way to solve the problems caused in either direction, to strike balance, and then to move on again.
I'd suggest that people that don't like change are living in the wrong country.