Why does a cultural region change faster than a physical region?

Culture (people) includes religion, folkways, foods, language. People can suddenly move to another area leaving open that area for another culture or similar culture... war, disease, and famine can erase certain cultures. The Mayan culture disappeared mysteriously. The Aztecs were absorbed via Spanish occupation.

By physical you mean geography and geology. The Earth does change but a region or physical regions (i.e. southeastern U.S., Pampas of Argentina) arr without established borders. Physical change would require a climatic change via earthquake, volcanic activity, asteroid strike changing the landscape.