Slavery was a business, in spite of how brutal it was, we still cannot overlook the fact that it was a business. It wasn’t just about punishing the enslaved; it included making a profit. The strategy of obtaining free/cheap labor has never changed throughout history. Regardless of the evil that was involved in slavery, the enslavers were not going to conduct this business in a manner that would be a liability to their operation. With that said… no one is going to take people from a foreign land, and then bring them to another foreign land to enslave them for profit. That would be a major liability for the enslavers because it would restricts their control over their business.
Slavery was enforced primarily by European colonialists, and the nature in which they colonize and obtain free/cheap labor has always been the same. Either they bring the workers/the enslaved to their mainlands, where they can establish control, or they infiltrate an already established government and manipulate it in accordance with their will. If you should study history and the reputation of the European colonialists you will see the proof of this pattern.
Most people are more focused on the emotional aspects of slavery and it is causing them to believe things that are just unrealistic and this creates confusion.