It's really about money as DynaLo says. Building a nuclear plant is a huge investment, and there are many across the US that were never completed - TVA has a few of those sunk investments. When a couple of cowboys with a modified jet engine and cheap natural gas could generate electric power cheaply, it put a stake in the nuclear power heart. We'll pay the price now for that short sightedness (whether we blame the investment community, the utilities, or the "renewables" crowd) because you may start a new NG fired plant, solar farm, or bird shredders almost overnight but you can't do the same with a nuclear plant.
The other thing that nobody seems to be talking about but looks like disaster in the making for long term and certified technology is electronics obsolescence. You can't just replace forty year old transistors in nuclear plants if they don't exist and nobody wants to manufacture old parts. Regulations mean you can't buy off the shelf replacement components or systems to keep a plant running when electronics manufacturers are thinking a couple of years for obsolescence of new devices.