My theory is that the Maya collapsed because of malnourishment and all of their sacrifices. 80% of Mayan skeletons found show signs of anemia, which is a condition where the body does not have enough healthy red blood cells. There are also many skulls found which show signs of malnourishment. Now people still do live in Copán valley, and the farmers say that crops are scarce and that the soil is not good. If the Maya were already malnourished, all of the sacrifices they made would not have helped their population. The Maya sacrificed all of the strong people, all of the tough people, all of the hardworking people, and more. With the people that were strong and tough gone, the rest of the population could not as easily defend themselves from animals or other humans, nor could they endure as much as the toughest people could. With the best farmers and hunters sacrificed it was harder for the Maya to get their food, which would lead to malnourishment.
Two Mayan skulls both showing signs of malnourishment and anemia.
