As the article states, they lost their competency. Here in France, the reason is poor planning, focus on cost-cutting and lack of long term vision by top management and government. EDF, the historical state power company turned into a private company in 2004, laid off most of the technicians that built the power plants over the years and subcontracted all the maintenance work to hundreds of subcontractors that fight for the lowest bid and employ only underqualified people, who often work in illegal conditions. The latest EPR reactor in construction in France is riddled with defects, the pressure vessel, built by Framatome, also absorbed by EDF, has uneven carbon content which means it could crack. The concrete enclosure has many large holes due to poor work. The bridge on top of the reactor was made of low-quality steel bought in Russia and had to be replaced. Basically everything is badly done, because they constantly try too make it in the cheapest way possible. But it's not working out for them because fortunately the nuclear safety authority is there to force them to redo things correctly. In its current state, the nuclear industry is basically dead in France. As another example, they can't decomission the plants arriving in end of life, and EDF officially postponed it until 2100.