Why do people eat meat?
Because from the beginning of time, that's what we eat. That was until people found out that you can eat peanuts to substitute meat. But there are a few people, like me, that are allergic to peanuts, or all types, and we have no choice if we want to be vegan or not. I have to eat meat, if I want to or not.
Eating meat is a natural food source for Vitamin B 12 as well as a number of micro nutrients not naturally occurring in other food types. It is the reason that humans have grown and developed over the millennium and that human brains have developed to the level they are. Without meat human's have to fall back on artificial sources of many of these which may have long term negative effects.
We are fed meat when we are too young to make any choices concerning our health, or anything else. Eating meat becomes a habit, a tradition or a learned behavior; also, whenever we go to a restaurant, meat is usually considered to be the main dish so society has a great deal to do with this issue. When we become adults, it is a personal choice to eat meat or to abstain from it.