It's far, far more expensive than renewable energy. It also takes far, far longer to build a plant. Too long to meet 2030 targets even if you started building today. And in most western democracies you wouldn't even be able to get anything done by 2040 if you also add in political processes, consultation, and design of the plant.
There's a reason the current biggest proponents of nuclear energy are people and parties who previously were open climate change deniers. Deciding to go to nuclear will give fossil fuel companies maximum time to keep doing their thing. Companies which made their existence on the back of fossil fuels, like mining companies and plant operators also love it, because it doesn't require much of a change from their current business model.