We have hundreds of years of history where civilizations have concluded that white roofs are cooler. We have decades of modern academic research that backs that up.
One study indicating the opposite may be true in some cases is not sufficient evidence to start overturning legislation. It's not enough to start submitting to the lobbying of these huge corporations trying to sell darker roofing materials. It IS enough to call for more research into the matter, and if enough research confirms this new finding THEN we start changing laws.