Indoctrination.
In the US, dependent on location, a person may be living under several different governments.
Governments recognize and/or create holidays, and holidays can go on to be cultural events.
Governments organize and finance festivals and events, which can and do become culture of a place or people.
They built statues, museums, parks, libraries, theatres, etc; all with several different levels and layers of culture.
You'd need to start defining parameters of what is a government, what is a culture shift, etc.
That doesn't mean they can't, won't, and don't, shift cultures in many other ways.