Outlining a few, in no particular order, that are probably relevant to your comparison between the US and India (although I don't know India as well): 1) Public sector employees in the United States are relatively well compensated, such that they don't need to supplement their income with bribes, and the fear of losing their job is a significant deterrent.
2) There are laws that prevent politicians from firing civil servants and giving the jobs to their supporters (this was not the case 200 years ago), so patronage networks are less powerful.
3) There are relatively effective checks on large scale corruption through independent layers of law enforcement agencies and a separate judicial system.
4) The state has relatively less control over the lives of ordinary citizens, so there are relatively fewer opportunities to extract rents.
5) There is a very engaged, sophisticated civil society in the US with interests in keeping the rules of the game consistent and fair. Significant corruption will cause a significant backlash from these stakeholders.
6) The institutions in the United States are more established, and have spent more time developing the necessary checks, balances, and management norms that keep them free from corruption.
7) Cultural norms play an important role. There is a theory that knowing the rules of the game and consistently applying them is more important than the level of corruption. In many countries, corruption is simply "the way things are done."