Accelerating Alt Energy Adoption: Local Government Mandates & New Home Construction

Disclaimer: I make shit up for a living. This begins with a "what if" followed by a "why not." I am by no means savvy in the fields of politics, construction, environmental engineering, or most realms of reality. However, I am vastly interested in the answers to stray thoughts of "what nots" and "if whys."

Image from: http://www.envirogadget.com

Today's Question:

Why don't local governments mandate alternate/renewable energy sources be built in to every bit of new construction?

My curiosity is piqued by this post from Sci-Fi Author Tobias Bucknell: Solar Power has a Moore's Law? Political backscratching aside, is there a reason why new homes/offices aren't built to be self-sustaining/nearly self-sustaining with solar/wind/water/geo-thermal/whatever-resource-is-location-applicable?

• Is it the input cost? Wouldn't economies of scale resolve that?
• Is it the output cost? Would builders be unable to sell new construction at a profit? Couldn't  dreaded temporary subsidies offset that?
• Is it consumer desire/demand? Good marketing convinced an entire nation to pay for water. If the only new-construction home you can buy is one that will cost you less to heat/cool/power, doesn't that kind of make its own sales pitch?
• Is it institutionalism? There's no doubt that the utility providers would take financial hits as consumer demand declined. The support industries would also suffer. Greed does wonders for innovation, as does demand for alt-energy supplies and maintenance.

As the weather warms, I think of the rolling blackouts for densely populated areas. I think of the doodad on my AC that automatically cuts out at energy-company-determined intervals to prevent the local power grid from overloading. I drive down my neighborhood streets and gawk at the new homes under construction. I can't help but wonder if every old house torn down to build something new was rebuilt to be at least 3/4 off-grid-capable, wouldn't that be better for consumers? Aren't governments the biggest consumers?

Yes, I completely understand why mandating retrofits will never fly, but natural churn could make a 50-year = 50% adoption plan feasible. Maybe? 

Local governments, for the most part, deal with all the permits, inspections, and nitnoids of construction in their jurisdictions. By logic, local governments are in the position to make this change happen. 

Educate me, why don't local governments mandate alternative-energy new construction?