Because it has only recently become cheaper to invest in solar rather than "ride out" existing coal investments.
I believe that the natural gas generators are still not at the "ditch as soon as you can" moment that hit coal hit a few years ago, and even then there's only so much solar being made right now.
The other factor is that solar manufacturing isn't being full-bore developed because as soon as you get a plant up, you're at risk of a paradigm shift beating you out. The promise of perovskites might be holding back silicon panel investment.
The Chinese, for as much as US media has been portraying them as a big bad, did a massive solid for the world in pushing solar panel manufacturing and battery manufacturing from the top down.
Granted they wanted to push everyone out/monopolize manufacturing, but who cares WHY, the net effect is to change our possible future for decarbonization. The US would never do that with the dominance of petroleum lobbying.
South Korea should also get a fair amount of credit for supporting Samsung in this direction.