Public choice theory is the application of economic theory to political science. It is about how government bureaucracies, which are created to serve a public purpose, change over time so that they serve the interests of the bureaucrats rather than the public.
This is something that in fact does happen, and it is a big problem. But it is not unique to government. It applies to armies, college faculties, priesthoods, labor unions, corporate management and any other kind of big organization, public or private.
It is possible to pass laws and regulations against corruption, but these laws and regulations will be ineffective unless most people have a moral compass that is backed up by public opinion.
A market economy is a good mechanism but it does not provide a moral foundation for society. Future executives are taught in Economics 101 that they have no responsibility to society at large but only to their stockholders and that the impersonal workings of the free market will make everything come out all right.
But if the free market makes everything come out all right, why should they even bother about the stockholders? Why should they not do what’s in their own self-interest regardless of the stockholders?