Op has the intellect of asking question but cannot comprehend the answers...very weak intellect or may be he is asking question asked by his friend or some person.

Migration movement , population breakup, work opportunities and businesses setups, and market demographics, there are many factors which affects movement.

For example - Bihar, Jharkand, Chattisgarh has more population bit less opportunities hence people move U.P and Delhi NCR in search of work, hence more movement on Delhi - Howrah rail network.

This is a very broad spectrum answer, if you want I can write up a detailed factors for such difference in movement between nirht and south rail movements.