1. The Democrats screwed up badly. They worked on running up the popular vote totals (in “blue” states) in order to a “mandate” and ignored the “purple states.” The Republicans focused on getting their voters out where it mattered and won the “purple” states. In the American system, a party should ignore states that you are certain to win or lose, and concentrate on the “in between” states. The Democrats must have thought we were using the French system (straight popular vote).
2. Please note that Hilary did not “win” the popular vote, she only had a plurality. The difference was in third party votes, particularly for the Libertarians. If we were using the French system, a runoff would have been required.
3, Also note that one reason for not using popular vote nationally is that states have different systems, e.g. some states let felons vote, others do not. Some states allow activists to collect absentee ballots and turn them in to be counted, and others do not. Also not that many of the big cities (New York and Chicago) are infamous for voter fraud, but in an electoral college system they only affect one state, not the national system.