How is this a tiny detail. We live in a passivhaus. We hardly ever heat. Improving insulation of old houses is an important aspect here. Reducing energy consumption is as important as generating and storing energy.
When the old homes decay to the point that they need to be torn down, then they will be. But destroying perfectly good houses is just too expensive in this market.
Only if the efficiency is 100%. In practice it's lower than that, so reducing consumption is better than increasing production.