The diet of the past was different from what we eat today.
In the past people didn’t eat much meat.
Prehistoric people ate fruit plants and from time to time insects. When they started to travel their diet changed and they started to eat nuts vegetables seeds and a little meat. The Aztecs and the Incas ate beans seeds cereals. In classical India people didn’t eat much meat and the Japanese were mainly vegetarian until a few generations ago. The slaves who built pyramids ate boiled anions.
However during the 19th century people in western countries suddenly began to eat meat.
New inventions like freezers helped to reduce the price of meat. Many people decide to become vegetarian, because it is healthful and killing animals is cruel.
Vegetarianism is very popular in present.