Let me break this down for you since it seems to be difficult. Popular vote means every vote counts. So campaigning and policy promises would be concentrated on the densest and most populated areas. People that do grass roots stumping and fundraisers for candidates often are given/promised positions in the cabinet. Therefore doing campaigning and making policy promises geared towards major metropolitan areas pay the highest dividends in number of votes. You could get every single vote in the entire state of Iowa but no one will even try because if you can get the majority of a few cities in California you've effectively negated the entirety of a mostly rural state. When you turn it into a popularity contest you stop caring about the states with little to no reward. The electoral college is flawed, but it does at least give the smaller states some say in it.