Each congressperson is looking out for their own individual interests. Their individual financial interests or their interests as it pertains to their individual desire for status, power, domination, sexual gratification, etc. that pursuit of individual self interest is an essential part of our culture. So essential, in fact, that we are told it’s a fundamental part of human nature. We are told that every individual human is a rational actor pursuing their own self interest, even in a very machiavellian way. Congresspeople are no exception.