The primary reason there were fewer slaves in the backcountry of the Southern colonies than in areas closer to the coast is that colonists in the backcountry were primarily self-sufficient.
Backcountry settlements often relied on subsistence farming, where families grew what they needed for survival rather than producing cash crops that required a large labor force. In coastal areas, plantations cultivating crops like tobacco, rice, and indigo relied heavily on slave labor, which is why those regions had higher numbers of enslaved individuals. In contrast, the backcountry's geographic and economic conditions made slave labor less necessary and less feasible.