Plant Vogtle was approved by the Atomic Energy Commission (the predecessor to the NRC). Their license was grandfathered in. Building this reactor required a new reactor license (not plant license). Shortly after the reactor design was approved and construction started, the federal government added new rules about containment vessels being resilient to passenger aircraft impact. The NRC applied these rules retroactively, causing the containment vessel to be redesigned and construction to be halted.[1] The companies working with the NRC are reluctant to criticize regulators, as they fear retaliation from the NRC. The NRC supervises and approves each step of nuclear reactor construction, making it very difficult to schedule work with contractors and suppliers. Honestly, it's amazing this plant was built at all.
1. https://www.ans.org/news/article-1646/root-cause-of-vogtle-a...