It is easy to know howthe South failed to change, but it is harder to know for sure whyit did not.  If we knew for sure how to change and improve economies, we would do it and there would be much less in the way of economic problems.

That said, we can make a few conjectures about why the South failed to industrialize or to mechanize its agriculture.  Some possible answers include:

• Too much competition from the North.  The North already had well-entrenched factories and these made it hard for new Southern factories to compete.
• Northern domination of railroads.  The railroads set rates that discriminated against Southern goods moving towards the North.  They charged more for these goods, thus hurting the South.
• Large supply of cheap and unskilled labor. This made it so that landlords had much less need to mechanize their agriculture.  They could still make money using a sharecropping or a crop-lien system.  This made development less necessary.

All of these are possible reasons why the South did not experience as much economic change as some might have hoped during Reconstruction.

Why didn't the South change economically during the Reconstruction period?

It is also interesting to contemplate the state of the South before the Civil War more or less destroyed it--because from the very beginning, it was economically very far behind the North.  Indeed, economic differences, and the resulting conflicts over economic policy had been one of the many things that kept sectional tension escalating as the nation expanded.  When the war began, the North had overwhelming advantages in nearly every area:  a population twice as great (21 million to just under ten million, with about a third of that being slaves), occupying 23 Northern states to the South's eleven.  Then when one looked at the products and processes used to carry on war, the advantages become even more sobering, because the North claimed manufacture of well over ninety percent of the firearms, locomotives, fabric and pig iron.  The North had twice as much railroad laid as the South, and it controlled the United States Navy.  The South, economically, had been stagnant for years in terms of developing new technologies and investing in industry; some far-sighted Southerners saw the writing on the wall before the war and attempted to get others to listen to the need to look at some new economic ideas, but as sectional hostilities flared, more and more people in power just didn't want to hear it.  Emotions took over, and a mythology developed that the issue was protecting a way of life--albeit one which was rapidly going out of style, more or less, as industrialized nations forged ahead into an era that was unlike anything the world had ever seen before.

Thus, when looking at why the South did not change as much as it could or should have, it's important to consider how very far behind it was in terms of economics, technology, investments, and "progress".  It might be argued that the South didn't change after the war partly because it didn't want to, i.e. creating the sharecropping system was a legal way to adapt the old economy to the new situation; but also, one might theorize that the South didn't know how to change, that it was so terribly behind the rapidly industrializing North and Great Britain before the war, that once it was virtually destroyed and forced to start completely over, the only way anyone knew to begin to scratch out a living was to try to emulate in whatever way possible the old economy.  Recovery must precede reformation, i.e. developing effective new policies is probably not possible when the people are simply trying to survive. 

I don't believe the social factors can be completly divorced from the economic situation, since the acceptance of African-Americans was forced an feelings of racism lingered long into the 20th century.

With that being said, there were many reasons Reconstruction did not revolutionize the economy of the south as many had hoped.  First of all, the war ravaged the south, especially some of the total war practices seen at the hands of later commanders such as Gen. Sherman.  Fields were destroyed, livestock was killed, and infrastructure such as railroads were rendered useless.  Additionally, hundreds of thousands of men died, severely limiting the labor force of the south.

The loss of the railroad was especially damaging, since the focus of the nation was on building the transcontinental railroad and not rebuilding the damaged lines in the South.  Without that lifeline, the south would never be able to transcend its agricultural roots.

Most of all, there was still an incredible demand for southern cotton worldwide, and with big money to be made many were uninterested in an economic transformation.  Actually, much effort was made to keep the old system in place playing by new rules.  Sharecropping enabled land owners maintain control of their lands and laborors developing a system akin to serfs in medieval Europe.  Black codes were put into place to maintain the heirarchy present before the war.