A slave is personal property. And as such, the owner of the slave has paid for an investment and expects the investment to grow. Slaves were mistreated in many cases but treated well in many more. In the US in the late 18th and 19th centuries, a slave was a valuable commodity and thus only the wealthy plantation owners had more than a couple slaves. Poor sharecroppers could not afford a slave, and those that did well enough to purchase a couple slaves could ill afford for them to die or be unable to work because of mistreatment.