Their prey went to shallow waters and orca's/great white were the only ones to reach them. The ice age decreased their prey sizes aswell in the end the only things they could find to eat was another Megalodon and basically killed their own species.
Yeah, something that big would have required a huge amount of food to survive, so disruption to its food supply would be fatal. There were likely a whole host of contributing factors, but shortages of suitable prey and climate change were probably the leading causes.
Bet with Liquidlaser: I say PS5 and Xbox Series will sell more than 56 million combined by the end of 2023.