Because many of these effects are so minimal they wouldn't even pay the cost of preparation. Residential energy credits, excluding exotic things like geothermal, are limited to $500, but the preparer has to examine all previous credits dating back to 2007. Speaking only for myself, most of my long-time customers who would upgrade for energy have used up their credits long ago.
Reviving some of these credits would help a small percentage of energy-conscious taxpayers because of prior usage.
Being conservative, I do worry about the huge deficit. I wish some of these lobbyists fighting for these goodies would figure out a way to pay for them. Not partisan political here, each party is as bad as the other re: spending.