Slow, expensive, more carbon emissions than renewables. Either nuclear weapon proliferation or corruption, there is no other reason to build reactors...
There isn't a perfect energy source, that all countries can use to transition to green energy. Not all countries have access to great conditions to harness solar or wind efficiently or have easy access to hydro. Europe is investing heavily into interconnectivity to take advantage of each country geographical strengths.
And nuclear energy is on a rise. SMRs negates all the downsizes of the old, sketchy nuclear plants, and companies are already buying into them.
Nuclear is basically the only viable large scale replacement for base load generation to replace carbon fuels like coal and natural gas.
Things like solar and wind are great, when they can generate, and grid scale batteries can help with balancing and peaks to an extent, but the base load is an issue that they just cannot address.