The Electoral College does this because it causes our presidential elections to be decided on a state by state basis. The national popular vote (as seen in the election of 2000, among others) does not mean anything.
In our system, each state's popular vote affects its electoral votes. In almost all states, whoever wins the popular vote gets all of the state's electoral votes. This happens even if the candidate who wins the state only wins by 1 vote.
In reality, the state by state results are the only ones that matter. They determine who gets the electoral votes. The electoral votes determine who wins the presidency. In this way, the election can be seen as 50 separate elections (and one in the District of Columbia) rather than one big national election.