What causes people to kill anamals?

It is for a variety of reasons like:

survival/food

mating

Obviously, for survival they want food, so they prey on other animals. Also, they kill other animals for survival if the animal is the one being preyed on.

Interestingly for mating, usually male animals fight each other for a female to show that they are the strongest (which means they have better genetics). So whichever male animal comes out the strongest, they mate with the female.