That is often the case all cultures are changing modeling, disappearing or creating in the long human history no matter what culture is concerned. Culture is a way of people living and working to solve the problem in order the human to make a better life, as a result culture must change with time since human beings are expecting to have a better future then there is no wonder some of the cultures on Earth have gone with extinction. It is a natural course of evolution that we have to accept even if some people disagree in their feelings. 

Scholars always pay more attention to external factors than the culture per se. One good reason is that maybe the culture's successors, the people simply don't like it that much.