Candidates campaign differently in order to win electoral college votes. And most likely people's choice wether to vote or not is influenced by this system.

for example, a Trump supporter in California might not bother to vote at all, knowing their state isn't go to elect their candidate anyway, so that's less votes overall that go away. It also works the other way around too. Many people will vote 3rd party as a protest vote, if they don't live in a swing state but would otherwise have went with one of the major candidates had the popular vote been the way to win. So it still isn't clear that the final outcome would've been the same or different.