The Electoral College exists for a similar reason the Senate exists.
The Senate was created to give each state equal representation. Otherwise, the populous states would get to pass all the laws and get all the goodies. Remove the Senate, and the less populated States would be totally justified in leaving the Union. Hence why they demanded the Senate be in the Constitution in the first place.
If we do not have the Electoral College, then again the popular states/cities get to elect the PotUS. Essentially, making it if you did not live on taller peaks on this map (http://i.imgur.com/mcA2hWa.jpg), then you would not have a voice in choosing the PotUS. Why would less populated States ever agree to make themselves irrelevant?
The question is: Is there a reason for these smaller, less populated areas to have a voice in government? Yes. The reason is that these areas are where our natural resources come from. It is also where your food comes from. Large population centers would be impossible without them. In that way, they already have a certain power over the population centers. The Senate and Electoral Collage recognize this fact and give them some representation. Probably less than they are really due.