Wikipedia says the plants are managed by EDF, a private company. Ordinary asset management would have prevented known problems, so there must be a few things that went wrong at the same time.
* It has to make money, instead of being a utility that the state provides, so decisions have to be taken in accord with all shareholders.
* When it does make these decision, well, politicians have been selling off EDF piece by piece on the right, and sacrificing it to get votes from the green party on the left.
All in all, incompetent fucks with a 5 year foresight running it like a pawn on a chessboard, happily sacrificing it to get a meager advantage.