I think some people won't be happy until we're all constrained to 10x10x8' rooms in 80 story buildings to satiate their desire for density and efficiency. Maybe we should just kind of be happy with 7 billion people.
Perhaps people like living in smaller quarters in cities - the market seems to indicate that, based on the price per square foot people are willing to pay for urban apartments compared with ... anyplace else in the world.
(I'm in a 1400 sq ft / 130 m^2 2/2 apt in ATX.)