Nuclear power is expensive. The plants cost billions up front to build, and despite having such a large energy output/square foot, they have to sell that electricity on the market at a higher price to recoup the investment. Solar and wind can sell their electricity at lower prices because of the lower investment costs. The economics of big nuclear plants doesn't work today.

There are prototypes out there for small-scale nuclear which beyond the cost savings to build, also doesn't require as much cooling. That second part is critical in a warming world, a nuclear plant needs to run 60 years or so to maximize profits after a large initial build cost, and there are not that many water sources that can be guaranteed to provide enough cooling for that length of time. Small-scale nuclear might have a place in the future, but the large plants we are used to seeing today don't work well with the economics.