I think the biggest reason it hasn't been changed is because it presents the opposite problem if they move to popular vote. Small states will lose their "voice" because campaigns will focus on areas with dense population [L.A, N.Y, Chicago, etc].
Yes and no. Yes, campaigns will start to visit more populated areas if the electoral college is gone but, unless they candidates are morons, they'll need to pay visits to much more states because about 80% of Americans reside in locales with less than 200 000 habitants, so winning with only the metropolis' votes won't make any candidate president. Also, with the electoral college gone, the winner-take-all system in each state will probably be gone too, so candidates can't rely on "blue and red states" and have to make every vote count for them.