I would also add c) Many people feel that the popular vote is what should be important. For example, polls in the media almost always report the popular vote tallies and nothing deeper, with the assumption that the Electoral College result will follow. Historically, this has been true the vast majority of the time. The Electoral College has only gone against the popular vote five times, and before Bush 43, the last time it happened was all the way back in 1888.

The more the Electoral College diverges from the popular vote, the better case you can make for changing the system. And on the other side, if somehow the counts were wrong and the popular vote did favor Trump, that would greatly undermine the argument for reform.

Also, going with the electoral college suppresses overall voter turnout in states that are "locks" like California, New York, Oklahoma, etc.

If I live in California, I'm less incentivized to show up for the election because I think of it as a lock. Obviously I should still show up to vote elsewhere on the ballot, but I may not because I won't influence the election.

If we were measuring by popular vote, turnout would be a lot higher and the outcome would, likely, be a better representation of the country.

Turnout would certainly be higher, but it's not clear that it would be a "better" representation of the country.

The electoral college distribute power, to some degree, based on geography. Geography is correlated with a large number of other "diversities" of American culture, from race, population density, to industry, to global warming risk, etc... Switching it to a straight majority would take power away from all of these subsets of society.

This election, it seems, it was "white rust belt" Americans that decided the election. In Gore vs Bush, it was Florida. Next time, it will be something else. It's all highly imperfect and somewhat random, but I see danger in solidifying power in what essentially will be people who live in cities.

As it stands, power is solidified in a dozen or so swing states, which make up about 20% of the country's population and aren't particularly representative. The electoral college isn't distributing power, it's concentrating power in a few fairly arbitrary places.

  In Gore vs Bush, it was Florida.

No, it was any state that Bush won. For example, had Gore won his own home state of TN, FL wouldn't have mattered. But any state shifting to Gore would have been enough.