One theory I believe is true is famine. Since they were in a drought, but they didn't know, they were still in a good start.
They used a 'slash and burn' style of make ing the soil better. Then they realized that the slash and burn didn't work for life. It only lasted for a few months, and it put the maya on risk of death.
A few months later.......
So it did. That would be a real reason why the Mayans died. They are all lying there, dead without eating food, and mothers, desperate trying to find food, for them and their babies.
Another theory is about warfare. They were probably on a fight, and had many more. There even might be a possibility that the people they were fighting with had armor, and were kind difficult to defeat.
Then after that, they get all tired and lay down and set up everything until it is under control. But then,, another, even harder to defeat troop of enemies come, and to that, they were to exhausted to fight.
Since they were so weak, one was slaved, the other was killed, and the mother and her kid ended up like slaves too, and that's why I think this theory is true.