The difference is that an existential climate crisis it just isn't treated by our leaders with the same importance as a good old fashioned war.
Because of environmentalists like Green Peace, Sierra Club etc.
Because the free market is not willing to bear the risks - even when you ignore the whole "nuclear waste" and "meltdown" part. The construction costs are extremely high and basically guaranteed to wildly exceed initial estimates, while electricity price is highly volatile.
The only way companies are interested in building reactors is by having a guaranteed government subsidy. For example, Sizewell C in the UK has negotiated a guaranteed electricity price of £119 / MWh. The long-term electricity spot price in the UK for 2013-2021 is closer to £70, so taxpayers have to pay an additional £49 / MWh in subsidies. Good luck selling that to the nuclear-skeptic taxpayers.