First, you can trivially store years of nuclear fuel, which you can't with fossil fuels.
Maybe this is already complete, but at one point of lot of it was from decommissioning nuclear weapons, so it wasn't "we need them for fuel", it was "lets make use of this waste material and provide a financial disincentive for nuclear proliferation".
Finally, the West has plenty of sources for Uranium, and given plants already have years of fuel onsite, it is never a pressing problem.
