This is a hypocritical decision on the part of the EPA, which just a week ago determined that its own proposed regulation wouldn't be enough to reach its 2040 emissions goal. Instead of making its rules even more robust, it's decided to play politics with the environment and roll back the already insufficient power plant regulation plan. The Earth is being polluted at dangerous levels, and the only way to fix it is by slashing greenhouse emissions.
Someone at the EPA must have finally realized that it wouldn't be a good idea to shut down 60% of the electric grid — which is essentially what would have happened since the original carbon policy was virtually impossible to follow. The EPA may have also noticed that the Biden administration is trying to double the size of the grid through his electric vehicle ambitions, which would ironically require more electric power, not less.