Why do stupid #NPPF Energy Viability Testing when the government has already done it?

Regarding the previous post why do viability testing when the government has already done a detailed cost-benefit analysis in 2009, the figures there suggest that with a nearly £300 saving on (then) energy bills for a 3 bed semi a part 4 standard would achieve payback in around 8 years, a nearly 300% IRR over a 25 year mortgage.  No problem with viability then.  So why waste everyone’s time.  The government research shows it pays for itself.

Indeed if the government really wanted to make housing more affordable they should lever the funding for mortgage deposits 3:1 by tax breaks equivalent to the additional energy savings costs.