Concrete and steel costs are negligible in the full costs of the nuclear plant. Complex machinery like turbines, reactors, etc have huge costs that fall of rapidly when you start mass producing them. If you make 2 plants/year the cost per item is X, if you make 100 plants/year the cost per item is X/10 or X/20. Huge part of costs goes into machinery that allows to build the thing. Once you have it, producing more parts becomes way easier.

Steam turbines are mature tech whose capex and opex are large and will not change. Likewise, high-pressure plumbing.

Thus, costs are not falling, and new starts are negligible. Even China, which asserts they will build 220 of them, has only started 10. The rest will be cancelled as their price is undercut, unless politics forces the matter. China is not cost- or value- driven. (Cf. "Ghost cities".)