Without this protection the voices of people who live outside the 5 major metropolitan areas simply wouldn't matter and candidates would have no reason to listen to their issues and have no repercussions for hurting them to favor city-dwellers.
This would be bad. Very bad. A straight population vote ends up being a scheduling algorithm for issues where rural interests have unbounded wait time.
One could say that the solution of weighting rural votes higher is a clunky system but any replacement voting system needs to take this into account as those small towns are where almost all of our primary industry is.