Obligatory: we didn't stop.
There's also good reasons to have a fistful of generation plants with coal or natural gas.
To put it simply, nuclear is clean, far cleaner than just about anything else we have. If you compare the waste product with the energy produced... It's just not an argument that nuclear loses versus something like coal. Where coal puts out its waste mainly in the form of smoke, nuclear waste, like discarded nuclear power rods, are a physical and far more immediately dangerous thing. The coal waste kind of blends in, and lobbyists have been throwing around "clean coal" for a while... Although coal use has gotten a lot more efficient and produces less waste than before, it's still far more than what nuclear could do. "Clean" coal is a myth, it's just "less bad" coal, with good marketing.
Regardless, coal and natural gas fired plants can ramp up and down far quicker than nuclear possibly could. Where nuclear covers base demand and can usually scale up and down a bit to help with higher load times, to cover peak demand, coal and natural gas can fire up and produce power in a matter of minutes. With nuclear, they have to ramp up slowly to ensure the reaction doesn't run away from them, and to ensure all the safety measures and safeguards are working as intended as the load increases. It's just a fat more careful process.
The grid is hugely complex, and I'm simplifying significantly. But from the best of my understanding, nuclear can't react fast enough to cover spontaneous demand. So either coal or natural gas needs to exist for the grid to work as well as it does.
Wind is unpredictable and solar usually isn't helping during the hours where the grid would need help with the demand. The only viable option is with grid scale energy storage, which can hold the loads while the nuclear systems have a chance to ramp up.
There's still far more coal fired plants in the world than we need for this task alone, so there's still work to be done... But I suspect coal use will diminish, but not be eliminated from grid scale operation for a while.
