Why do you think both the federal and the states government were given the power to collect taxes

Well in order to maintain programs (health care, military costs, social security, ect.), each citizen is required to pay a portion of their income in order to keep these very expensive programs running. Each state in turn has their own individual programs which fall strictly under state jurisdiction (not under federal control) and so states also tax citizens (18 & up) in that state to support their own programs.