Why do we only give disproportionate representation to people on the basis of their zip code?
Why not give disproportional representation to them on the basis of their race, or religion, or sexual orientation, or on whether or not they prefer big, or little-endian notation? Surely, it would only be appropriate that politicians should have cross-demographic appeal to win?
Every argument for why we should give extra influence to voters living in particular zip codes is just as valid, as any argument for giving extra influence to voters based on some other semi-arbitrary distinction.
Rural people have special, marginalized concerns, and are outnumbered by urban voters? Great. So do LGBT people, for example.
You don't get extra consideration for your vote for being a ______. Why should you get it on the basis of geography?