Why were slave owners so mean to slaves?

The slave owners so mean to slave because of their skin color that's why and they

thought they were different.

Also beating the slaves showed power and dominance over them. And beating slaves, and pushing them to their maximum efforts proved for them to be cheap and efficient. Another reason why a slave owner would be cruel to a slave would be to take out some anger or for hobby/sport, or for some other emotional to psychological reason.