Why didn't they?
it could have considerably shortened the war!!!!
At a guess, I'd say: Because they chose to destroy, or attempt to destroy, the industries
that would have run on said plants and the logistics that fed them. Factories that get no fuel or spare parts or raw materials won't have much use for electricity, even if they themselves survive the attacks.
Further, a lot of big factories back in the day had their power plants built in - bombers had to destroy the factories anyway. I've seen this in industrial photos from the era, and I expect it would have been a factor in Germany too.
So no, specifically targeting power plants wouldn't have had the bigger effect you expect.