True, but they do change; if e.g. an empire hangs around for long enough, the original culture will be lost or assimilated. See for example Christianity throughout Europe, plenty of examples of erased or merged cultures to the point where nobody knows what happened before. Or the lasting influence of colonization throughout the world. Or the change of culture and language that the US has throughout the Hollywood media-consuming world; listen to random people in western Europe and count how many Anglicisms they use in their native language.
Some more examples:
- apparently ancient Egyptians had this problem with their own past, but I don’t remember where I read this. If anyone has a source, I would be thankful.
- pre-indoeuropean language families in Europe, only Basque remained that we know of
