Southerners had short, mild winters. Long rainfalls & long growing seasons were ideal for growing warm weather crops. The South was plentiful with swamps and marshes, and broad flat rivers. South's earliest towns were built at the mouth of rivers.
The South's climate was perfect for crops and it still is. The South is still used for crops being traded around the US due to their perfect crop growing weather. Water travel is not used as much as it used to be but it is still used sometimes.