Answer:
In 17th century America, physical labor such as farming was very hard work, even harder than labor nowadays. The South especially had it rough because they weren't as industrialized as the north was, so farms were a big deal, but they needed extra help working on their farms. The only problem is that hiring a lot of farm hands to help tend to the farms could get pretty expensive. Slaves were a way for the South to reproduce their crops and not have to pay their workers or give them too much of what they grew. Even though it was bad news for the slaves, farmers and others were able to profit off of the slaves work and expand their businesses.
Hope this makes sense to you.