> Voter fraud is easier in big cities. <
Thanks to the genius of the Electoral College, that voter fraud cannot cross state lines. It can corrupt, at most, the state where that city is located.
Get rid of the EC, and voter fraud in Los Angeles, Chicago, etc. will impact the entire country.
Even with the Electoral College, voter fraud in Chicago and Texas in 1960 did impact the country. But without the Electoral College the situation would be much worse.
It would be worse than that. There would be an arms race between states to increase the number of popular votes from that state. What would stop California from enfranchising every illegal immigrant in the state? Or to give the vote to convicted felons and everyone over the age of 12?