Electoral votes are a way of normalizing voting patterns across states.

It's similar to the reason why there is a separate Congress and Senate, to try and balance proportional representation with state representation.

Focusing on the popular vote is actually very misleading, because many americans do exactly what you are proposing: republicans in heavily blue districts don't bother voting, and Democrats in heavily red states don't bother voting. They should (so that we get a better understanding of support) but it is a waste of time. If it was a direct vote, you might see increased Republican votes in California and New York, and increased Democrat votes in red districts.