Because there is absolutely no reason not to assume that those new nuclear power plants will once again take least 20 years to build (and will be 3 times over budget). That's quite a long time span that you need to fill with fossil fuels.
Political will requires a median IQ high enough to understand the tradeoffs and lack fear from decades pass, which I don't think is possible this century.
The only reason countries want to maintain an industrial nuclear supply chain and skills base is because they are a nuclear power already (France, Russia, US, etc.) or because they are purchasing the option to become one in a hurry (Iran, Sweden, South Korea, etc.).
Governments don't firehose subsidies at a form of power that has an LCOE 5x the cost of its competitors and give it free catastrophe insurance on top for the hell of it.
People will post stuff like this and then act surprised when others are put off.