Slavery was based on making money. Plantation owners wanted workers to harvest the crops and take care of the land. They would do the grueling work on a farm. They worked long hours in the hot sun. The owners would make a lot of money because they were not having to pay for their workers. Instead, they merely made these people live poor lives. Then the owners collected money of all the profits they would collect from their crops.
Instead, they made large amounts of money and they continued to make lots of money due to the laws. The laws allowed for slavery and over time more and more states stopped slavery and would not allow it. However, it took a matter of years before slavery stopped and plantation owners had to do the right things and hire workers and pay them.