Robert Anton Wilson explained this years ago:
The capacity to learn from others is one of the traits that have made humans such a global success story. Relying on it too much, however, could have contributed to the demise of past populations, such as the Maya of southern Mexico in the eighth and ninth centuries and Norse settlers in Greenland 1,000 years ago.
Over-hunting, deforestation and over-population are well-worn routes to societal collapse. Now, Hal Whitehead of Dalhousie University, Halifax, Nova Scotia, Canada, and Pete Richerson of the University of California, Davis, have modelled how different learning strategies fare in different environments. They found that conformist social learning — imitating and emulating what the majority are doing — may also cause the demise of societies. When environments remain stable for long periods, behaviour can become disconnected from environmental demands, so that when change does come, the effects are catastrophic1.
Environments often change in unpredictable ways and over timescales from the seasonal to millennial. Rainfall and temperature change both seasonally and annually; populations of predators, prey and pests rise and fall; soil conditions change.