And where is most of the american population concentrated?

Cities like NYC, LA, Chicago, etc. National elections are not about the individual, its about the collective. It's not about the worth of the individual's vote, its about the worth of the collective vote of the community. And in a popular vote, the collective vote of the cities would drastically outpower the collective vote of rural communities. And it's almost never near 50/50, it's usually 70/30 or even 75/25 in these areas. Wyoming and West Virginia doesn't have any big cities, almost all rural areas with some small towns, and their vote is around 70/30. Maryland and Massachusetts have many urban and suburban areas in a relatively small area leaving little room for rural communities, and vote heavily democratic.

The EC attempts to mitigate the overwhelming power of big cities. That's why we have a senate and not just a house of representatives.