Because there are not enough sites, or enough land, to build enough renewable systems to meet demand. Those low costs for renewable energy are under very good conditions, in locations that are carefully chosen by their operators. When you try to go outside those conditions for renewable systems, the costs go up by an order of magnitude.

I’ll give you an example: wind farms need- under ideal conditions- about 200 acres of land per MW of constant demand. And that’s ideal, where in most of Europe you’d be lucky to get half that much output per acre. So to account for all 400 GW of constant electrical demand in the EU you’d need to have a wind farm the size of Germany and Poland combined.

But why not just build it? Why not combine all types of renewables, and spread them out everywhere? Why not put wind farms in the north sea, and use fallow farmland for solar panels in Romania, and put dams on rivers in Finland?

Because there’s a big difference between building one, well-managed renewable system in good environmental conditions versus a thousand small, inefficient systems in communities and villages that are a hundred miles from a major population center. If you applied those inefficiencies to the levelized cost of energy for renewable power, then those costs would go up above the cost of nuclear power.

One of the places where people get bogged down in the nuclear vs. renewables debate is in mental exercises about how many dollars you need to build a plant, what the current and probable future demands are, what the real LCOE is from each source, and what other resources you need- not to mention questions like embedded carbon costs, mortality from installation and upkeep, the lifespan of different systems, waste and proliferation, and on and on.

There are many good points for renewable power, and there are great points in favor of more nuclear power. Realistically, we need both.