Why China is building so many coal plants despite its solar and wind "boom?"

[thought crime]

1. Absurd question. Obviously, China's energy growth demand exceeds supply from any one single technology

Renewable energy is growing by leaps and bounds in China but it would be absolutely absurd to expect that it could currently begin to keep up with China's fast growing energy demand by itself. But eventually renewable energy will go a long ways to replacing coal.

Given your position, the question you should consider is, "Why is China building so many coal plants despite increasing the number of nuclear plants?". Do you think nuclear energy could currently begin to keep up with China's fast growing energy demand by itself?
Of course not. It doesn't, can't, and won't. A single source of energy won't cut it any time soon. A transition to 100% nuclear energy that you advocate would take a very long time and the cost would be prohibitive.

Your question is absurd and the answer is so obvious it throws suspicion on your motive.