* Plants are very expensive to build. Due to massive upfront costs, it cannot beat wind/solar today unless you use very unusual financial models. (ie. assume interest rates are zero for 50 years). If nuclear plants were built more frequently, cost would come down a lot - it turns out making everything bespoke is hugely expensive.

* Lots of public opposition due to the public being scared of nuclear waste, nuclear accidents, etc. The public far prefers taking on invisible risk (like the lung cancer risk from coal/oil/gas emissions) than the huge event risk of a nuclear meltdown, even if the overall harm to human lives is higher.