It's backup power. The power plants will never pay for themselves, but they enable much wider solar deployment because you can use the plants the 1 day a year when the whole country is cloudy.
Scroll through the last 72 hours here and you can kind of see it in action: https://app.electricitymaps.com/map/zone/CN/72h/hourly
Now, clearly, there's a long way to go, and China does still have a lot of baseload coal. But it's not building much if any _new_ baseload coal.
Think that's weird? France has load-following _nuclear_ plants (it more or less has to, given how much of its grid is nuclear).