The whole reason there is a United States of America is because each state would get a voice in choosing the president. By only going by popularity, a few select cities decide all. If it was proposed that way, the USA would never have formed and we'd have a bunch of individual separate countries.

Americans whose votes are counted in the current system have never changed that.

States representing a large majority of the US population have all passed legislation for a national popular vote, and no one doubts that a national popular vote on whether to have a national popular vote would succeed.