Answers (2)
Because the people just wouldn't stick to their principles. Very few were dedicated to any principle of freedom. Most were dedicated to the glory of a nation of their own. That is why so much of the nation's history involves the government breaking its own laws, such as giving land to homesteaders and then giving the same land to railroads. (And then regulating the railroads to death.) People keep telling you this is a free country, but only fools believe that.
The southern United States were largely agricultural; items such as Cotton, Peanuts, etc.
Large amounts of "people power" were needed to cultivate the fields for selling the grown crops.
The northern United States was largely industrial, not needing as much "field labor" for the factories.