Most professional archaeologists/anthropologists do ask the indigenous people and do listen. Sure there are always some people who are attention seekers, but the majority do good science and leverage indigenous knowledge. That said, you overestimate how much the people can know. They don’t have ground penetrating memory, and the Maya people have always been far from one united nation but closer to a collection of city-states with some shared cultural traits.

Furthermore, most of the classic Mayan sites were long ago abandoned so it isn’t like there are indigenous people hanging out around Ti’kal or Calak’mul that can just spill the entire history.

Any competent Mayanist would have told you the same as that person in Belize. It is no secret the landscape is dotted with unexcavated ruins, but the scope is unclear which is exactly why this research is so useful.