The Electoral College limits the impact of localized vote fraud.
Once you have illegally manufactured enough votes to win a state, there is currently no great advantage in manufacturing more votes. It runs up the popular vote total -- which is nice -- but it doesn't have any further impact on the election. It also provides a disincentive to illegally manufacture votes for a candidate in a state that he would win anyway like, say, Illinois.
But if you eliminate the Electoral College, then every illegal vote counts.
And I live next door to the city of Chicago.
Or as Joe Kennedy reputedly told his son, John, "I'm not buying one damn vote more than necessary -- I'm not paying for a landslide!"