Bombing strategy changed several times during the war. Sometimes it changed between one raid and the next. They never, for example, targeted power plants. They only did one bombing on a dam, despite the tremendous potential for secondary destruction. They went to area bombing because a study showed that only a few bombs got within five miles of their intended target. How would one bomb a mine? It’s already a hole in the ground.
I think you've got it. Bombs in those days were far less accurate than today.
These days, bombs are pin-point accurate, and the US even has a special power-plant bomb, the BLU-114B. It's designed to be used against the switching stations, not the generator halls. It works by dispersing a cloud of carbonized fibers over a substation or high-tension line. These cause shorts, blowing transformers and tripping breakers, taking down the enemy's power distribution system. Once the territory is occupied, having the generators themselves intact helps the recovery.
The conductive filament bomb was used in Serbia in 1999:
You watch the archival footage of B-17 raids and you will see many bombs falling in farmers’ fields. Navigation over enemy target areas was not the best back then. Precision guided munitions would have been considered science fiction at that time.