It matters because the president is supposed to be a nationally elected official. If he appeals to voters from a narrow geographic base, as al gore did, it's likely that he will lose, whether or not he won the national popular vote.
Also, can you reference a quote from the constitution that says the president is supposed to represent the people? Originally, electors weren't even appointed by popular vote, they were appointed by state legislatures.
That's not all. Very recently Baoky Vu , a republican elector from Georgia who balked on whether to support Donald Trump has resigned today says Reblican spokesman Ryan Mahoney. Vu had put out a statement in August saying that he cannot bring himself to vote for Trump in the November general election. And he might not have voted for Trump as a member of the electoral college, either. He suggested a write-in candidate but now he changed his mind and has resigned after probably being put under pressure by the Republican Party.
