Their point of departure is that societies are inherently resilient. They can be subject to shocks, even large shocks, and they bounce back. Yet, sometimes they do not. What makes this happen? The main point is that dynamics are important. It is believed that a severe drought was the trigger. But this civilization had such drought before and survived. The last one was different because it brought about systemic changes. There precise nature is difficult to determine, after all we do not know that much about Mayan history. One hypothesis is that the drought brought some unrest which made it worse. For example, agriculture used terraces, which are costly to maintain and rely on the good shape of the ones uphill. Under a severe drought, maintenance may have been lacking, and after some time the terracing system fell apart, and with it probably the structure of society. In short, there needs to be the dynamics of a death spiral for a collapse to happen, but it will still take some time.
That is from Economic Logic on a new paper that explores the collapse of the Mayan civilization.