Earlier quoted context omitted.
It is because money that would be building renewables that displace coal, oil and gas is instead tied up in construction, and not displacing any. When the project is finally cancelled, over budget and late, that money is spent and still not bringing renewables online. So, each nuke project eliminates substantial immediate, progressive, and permanent erosion of their market.
Developing effective renewables does not preclude the development of nuclear power. Switching completely to renewables in the very short term is not feasible, and it will take particularly long in areas that aren't well-suited to any of the main renewable power technologies. Also, many governments provide ridiculous fossil fuel subsidies, which should be eliminated, freeing up money. New nuclear power plants will pro…
Money is fungible. Each dollar tied up in nuke construction, plus each other in fossil fuel while waiting on it, are unavailable to use building out renewables.
(And, yes, I ignore the "nukes" thing. There is no confusion. The facts suffice to denigrate them.)