Because at one point in time the US played the dominant role here, with output comparable to entire continents. Now with globalization that dominance has shifted to Asia.
So in essence if there is a place that will convert to majority nuclear power it's most likely going to be Asia that still has the capability to do this. I don't think it's likely for the US.
US still has the capability for sure. Look at this environment in this country. Most every consumer good produced imported here without having to bear the externalities of local manufacturing or resource extraction like localized pollution and diminished health outcomes. Most money is kept or invested here. Most of the world is trying to immigrate here. Realistically if push came to shove this is exactly where you’d expect a massive buildout to occur. Supply of materials is solved with massive globalized trade networks oriented towards ports in NY and CA. Supply of money is solved from both private investors and also the strings the federal reserve can uniquely pull. Supply of labor is also solved considering how much low skilled labor is available in central and south America that is able to be drawn upon in probably a years time or much less if such job opportunities present themselves. There is also a lot of low skilled labor in this country already kept idle, working service jobs like cashiers in towns that have little other work but such service jobs, in effect the town exists and demands labor yet produces nothing, and these sorts of places were ripe for building out defense industries in record time in the 1940s. We import skilled labor and knowledge workers from most other countries who struggle to offer them lifelong work locally.
So in essence if there is a place that will convert to majority nuclear power it's most likely going to be Asia that still has the capability to do this. I don't think it's likely for the US.