Most of the comments here are speculative.
The TLDR is that coal plants have trouble ramping their production up/down quickly, unlike natural gas which can do so in minutes. So, if you have a grid that is being thrashed by variable production (renewables), this results in variable pricing and demand for baseload. Coal cannot economically compete in that market (and neither can nuclear, which has the same problem).
Why not put massive, grid scale batteries “behind the meter” at a nuclear or coal plant to enable continual production but only sell power when prices are high and store power when prices are low?
An analogy here is natural gas pipelines with intermediate storage caverns, which allow the pipelines to operate more steadily even if demand various greatly over the year.
Even better, if you have a functioning wholesale electricity market, you can put those batteries on the grid and benefit everybody.
But there are other storage ideas that do much better for that. For example, burning an e-fuel like hydrogen, or ultra low capex thermal storage.
Nuclear can load follow to some extent (my previous comment): https://news.ycombinator.com/item?id=36254716
But regulations and economics don't encourage it. Also note that NuScale appears to be designed to be dispatchable