My understanding (which is probably uninformed at best) has been that coal, nuclear, etc are used to cover base load, and basically work best when up and running at 100% all the time.
Natural gas has the advantage that it can be spun up and down pretty quickly, which has meant that it is used primarily for "peak" load, which I think used to be covered a lot of the time by things such as diesel and oil plants and have basically been supplanted at this point by natural gas.
Solar and wind have the trouble that they are unreliable, which means you need something to smooth out demand. This is something coal and nuclear are poor at, meaning if you are bringing solar and wind into the mix on a large scale, natural gas becomes even more appealing since you can spin it up / down to balance capacity.
A thing I don't see mentioned very often is the relative density of each power source. One of the things nuclear and coal have going for them, is that you can supply a lot of electricity in a fairly limited footprint.
Wind and solar a much less dense, meaning you need to cover a much larger area, and you need it to be more distributed rather than all concentrated in one place.
All of this is to say that I think everything is inter-related much more than people realize. Shifting to using more solar / wind creates a pressure to move away from coal / nuclear even without considering the "clean energy" aspect.