The answer is that companies have limited cash reserves and need external capital to do anything. Particularly when you are looking to build something hugely expensive that cannot generate revenue for years. The real "plant builder" is not the organisation with the technical expertise. It is the one that can pursuade banks and investors to take the risk.
I don't think you are disagreeing with parent. As you are explaining, "the market" thinks nuclear power plants to be too risky and too expensive compared to other power sources, which is exactly the reason why they shouldn't be build by public agencies anymore either.