The electoral college system ensures that individual states, including smaller states, have an impact on the election of the President and are not just overridden by large states. The creation of states' rights and the decentralization of power among those states is part and parcel to the electoral process that the founders envisioned.
A popular vote removes the power from the states entirely, placing it with the individual citizens. California's citizens don't vote as a block, they vote as individuals. Same for the citizens of Texas, Hawaii, and Wyoming. Far from being nationalized, the power to elect a President is decentralized. Conservative in California now cast votes that matter, as do liberals in Wyoming. The founders also envisioned power being retained by citizens and voters individually.