Whilst I agree with your broad point, climate change is a systems problem and requires systems thinking and systemic change.
If you make nuclear available, but it is not competitive with fossil fuel energy, then we will continue to use fossil fuel energy. A relatively small number of oil company executives with a profit motive are going to make this decision for everyone, directly and indirectly.
'Doing stuff', as you say, involves governments of the people heavily regulating the most powerful corporations on the planet to ensure they can't make this decision in the wrong direction.
Government action in this direction hasn't happened for the last 30 years, and doesn't look close to happening in the present.
As such, it's reasonable for climate change activists to make plans to meet the market where it's at and prioritise competitive renewable products above nuclear.