There are plenty of reasons why a powerful centralized state did not emerge in India after the collapse of the Gupta dynasty. Among the reasons is that unlike China, India is comprised of a multitude of ethnic groups and subcultures. So it has always been harder for an imperial dynasty to hold sway over the Indian subcontinent, than it has been for one to dominate in China. Although China also has minorities and subcultures, the overwhelming majority of people in Chinese domains are of the Han cultural and ethnic group.

Looking at the issue from a more in depth level, there were also specific peculiar issues surrounding the collapse of the Gupta dynasty that prevented the emergence of a centralized state. Let us examine some of the issues below:

1. The Gupta Empire consisted of a coalition of various states and nations held together through either military might or intermarriages. In the later part of the empire there were always constant rivalries and power plays among the various factions. These conflicts weakened the state cohesiveness and national unity which broke down central authority and made it all the more harder to keep the state together. 
2. The Gupta dynasty faced constant foreign threats and invasions which severely weakened its power. This in turn led to the empire breaking up into multiple rivaling states after the collapse of the dynasty, as the constant warfare had greatly diminished the national cohesiveness. So in short there was really no way for a new dynasty to take over a large unified state since the old state had totally disintegrated.  On the other hand in China most of the threats were internal in nature and when a new dynasty came into power, they were usually just overthrowing the old family while preserving all the other elements of the state.