Given the information that we have here, we are told that the Mayans were isolated due to the mountain ranges and surrounding natural barriers. This didn't allow for good trade routes for other civilizations. Due to such isolated conditions and harsh traveling environment, any other nearby civilizations would have not wanted to risk such perils for trade. The Mayans did in fact have natural resources, as we are told here that they used stone, bone, and wood in order to aid in the construction of their cities.
