It also tells the story that the energy price per mile is insignificant. Vehicles that use gas advertise miles per gallon because it significantly affects costs. They also advertise range (or maybe fuel tank capacity), but not as prominently.

An electric car's miles per energy is not as relevant, because current electricity prices are sufficiently low such that people won't really care whether it's 3 miles per kWh or 5 miles per kWh. They will care about how far they can go on a single charge, hence range is a metric that is often advertised.