How did megalodons die?

Answer 1

Here are some theories:

Food Shortages
During the ice age, Whales which were once prey to Megalodon went to the colder places where Megalodons couldn't follow because it was too cold. The whales had blubber which kept them warm.

Evolution
By the end of the Pliocene, the whales were getting quicker due to years of evolution and it became harder for the megalodons to hunt them.

Orcas
Killer whales started hunting in the same areas. When they were done eating, there wasn't much left for the Megalodon. The Orcas Also killed young megalodons.

Great Whites
Adults Great White Sharks which coexisted megalodon, preyed on Meg pups, or outcompeted Meg juveniles. They were more expereinced even though the pups were about the same size

Answer 2

The megaladon ate whales that lived at the time and when the the whales migrated to colder, shark free, waters the megaladons had nothing to eat and the population dropped till it made it to zero.