Have to consider meat digestion from a net calorie perspective. Eating raw meat is possible sure. But once you get to dense protein meats like a red meat, your body expends a lot of calories in the act of digesting it raw. Cooking it is like a pre-digestion step and allows your body to digest it with less energy expenditure.

It also probably was helpful for other reasons. You could store cooked meat easier/longer without refrigeration or kill off some of the bacteria and such making it healthier.