>Why are we so inefficient today?
We tend to one of a few extremes: a few buildings (often for show) are ultra-green and usually stuffy, others are meticulously space-optimized to maximize residency, and still others are vehemently individualist, a project (usually a house) built on a plot of land as though it were the only plot of land in the Universe. Projects in the last two categories tend to sacrifice energy efficiency because it is too expensive, in the one case because it reduces units per square inch and in the other because owner-built SFH usually optimize for a very idiosyncratic comfort/price ratio.
In the old days, construction was often managed by the army (viz. nobility), and designed at a town scale. Today, as part of a reaction to the crushing inhumanity of feudalism, we silo off our construction projects to preserve our individuality, or we "build by any means necessary" to make optimal use of what little space we haven't yet wasted. A compromise might eventually be reached.
In particular, a lot of old-school heat management relies on having some parts of a building extend high up in to the sky or down into the ground. That sort of construction is heavily regulated these days, by height zoning -- which tends to impose the same limit for a whole parcel, eradicating towers, chimneys and steeples -- and by the great deal of infrastructure underground (sewers, wires, etc). Incidentally, these regulations rule out the construction of the building we're looking at now -- you'd waste the entire "top floor" on a chimney! It would just not be cost-effective relative to a design that fills the zoning envelope with usable space.