Much of the land in the South was well-suited for plantation agriculture, which was the production of cash crops (tobacco, cotton, sugar, rice) for export. These types of crops required large amounts of labor, which was difficult to find in regions with a small population and a harsh climate.
Free Labor Shortage
In comparison, the climate and geography of the Northern states were more amenable to free labor. The North was more suited for small-scale farming of various types of crops, which would require fewer laborers. Furthermore, unlike much of the South, the North's climate would allow people to work outdoors year-round.
Availability of Enslaved People
The Atlantic Slave Trade had connected Europe, Africa, and the European colonies in the New World. Enslaved people from West Africa were brought to the Americas to be sold as chattel. Plantation agriculture in the South relied on the continued forced migration and enslavement of African people.