We call it the Mayan Mystery.
The mayan civilization fell but it's not like the mayans died because there are still maya people in Mexico today and it's still spoken language wise.
Some people think they just disappeared and like they're instantly gone but they left the cities. We have actually found some mayan cities that appeared to be abandoned almost immediately like food still on the table. So it's really kind of a mystery as to what happened. There was like a network of 50 cities and they were like engaged with one another and trade was going on and all of a sudden, it kind of just stops and we really don't know why.
Believe it or not, it wasn't until like 1920 that archaeologists realized that there was like this 1,000 year old civilization that had cities in Mexico.
So to answer your question, we can't know for sure what happened but this hasn't stopped people from making theories about what happened.
The most current thought is that it was probably a combination of things and they probably exhausted the land. There is evidence of a possible civil war that happened within the mayan culture. But it wasn't disease, it wasn't an invading army, and it wasn't a natural disaster. It seemed to be something internal but we're just not quite sure.