It's more like a mix of solar and wind energy investors with fossil burning energy investors, both benefit from shutting down nuclear reactors. Solar and wind investors just want to have their huge returns with nothing wasted, as each kWh is pretty expensive, but lacking nuclear power most of the energy generation will still go to burning fossils, who will profit massively from it. Happened in other countries too, like Ukraine, which was recently forced to temporary stop some reactors to benefit those two groups and of course make things worse for the climate.

The fundamental reason is electoral calculus. The socialists, and then macronists, needed green votes to get a majority. The safety assessment is perfectly fine.