- Because it specifies specific makes and models as qualifying the ability to use new technology is constrained
- It also assumes specific construction practices which often collide with other issues you might care about - like seismic construction
So instead of trying to minimize energy use per person living in the house we are forced to focus on energy use per square foot. So really big houses are better because you can have more internal volume (inside rooms, closets etc.) than a tiny house with relatively more windows.
The other problem of course is that the rules are complex enough that you have to hire 3rd parties to run the software to tell the permit people what your score is, which means of course that now we have a new special interest group that will lobby to insure that the rules never become simple.