Its a bad idea, because you are taking the saltwater marsh away from the ecosystem... And turning it into a cement covered ground, for more houses... Then the animals (or other things) that live there, will die... and have to find another place to live...
~therefore... The bad thing is, that they shouldnt fill the marsh with dirt, and cement... Because bad things could happen to the creatures that already live there.
The fact that the Mayans were building great buildings in their period of existence, is a proof that they had a very big political power in the region, and not just political, but also military, economic, cultural power.
Only civilizations that are strong, well organized, and political powerhouses, have been able to build such big structures, because they had the conditions and time for it. For building such big structures, lot of wealth is needed, also lot of workers, and great engineers. The Mayans had it all. They had great engineers, the labor force was provided in general by the slaves, or by the the tribes that they were ruling over, and from all the tributes paid to them by the people they ruled over, they had surplus of wealth, which meant that they can perform such activities without damaging the empire.
Geographers use map projections to translate the planet in a two dimensional representation. Unfortunately, you can’t display 3D surfaces perfectly in two dimensions, distortions always occur. There are many different projections that are commonly used throughout the world.
There are instances of low, rounded and subdued topographic features that sometimes being overlooked in the field and has not been seen or observed that's is why vertical exaggeration is necessary to enhance the measurement of height in models and presentation of terrains.