Part is the neoliberal economic model is really really bad at big projects. Part is the regulations and engineering complexity involved in not having them all shut down because they caught fire or the steam generators corroded (almost every program has "cheap" reactors at the beginning which have massive maintenance issues and leaks 10-30 years later, followed by expensive ones with massive delays). Part is corporate greed. Part is revealing and stopping rampant fraud and finding safety-compromising cost-cutting measures. Part is the lack of pressure from the military to make it happen as there is no longer a need for as much Plutonium. Part is that there actually are some semblance of environmental laws. Part is the fossil fuel industry interfering (as they do with all non-fossil-fuels).