In this case the Mayan society had already gotten to a point where they were able to build monuments that have lasted thousands of years. I am not that surprised that had incredibly sophisticated agriculture on a large scale because how else would they support a large population in the cities?
Building structures that last thousands of years is somewhat easy and the default once you start working with stone; many past civilizations have accomplished that. It's our modern civilization that optimized everything we do in a way that makes it not last long.
