The biggest scaling problems with nuclear are that we are building basically none of it right now so scaling it up means pretty much building the industrial base up from scratch, and the lack of qualified people which will need decades to train enough. It takes years to train up qualified nuclear technicians, and you'd need to scale up the schools too.

Meanwhile, the industrial base for wind and solar are massive now and increasing almost exponentially, and educating new workers takes months at most because there's nothing really complicated about them.