One suggestion I heard was that the Mayans were a bunch of imperialist tax collectors and their "empire" simply started refusing to pay tax when the military ad

One suggestion I heard was that the Mayans were a bunch of imperialist tax collectors and their "empire" simply started refusing to pay tax when the military advantages were no longer so important. You could probably say the same about Rome. Once everyone in the empire could out-Legionary the Romans (the provinces were the main source of military might anyway at this point), sending tribute suddenly became a bit of a waste of time. Any disruption can trigger a chain of revolts. A revolt could be armed, or a soft revolt where the locals start acting like feudal lords and claim it's necessary to keep the peace.