They've wanted to for decades, and now is their best opportunity to invade and take Taiwan. They see the US as weak in general and now on it's knees. Xi is in trouble internally and needs a war to hold power; he has little to lose and much to gain. He'll use the pandemic as a springboard, blaming the US for starting it.
Some others had the same idea. If they attacked us with this virus, and I'm convinced it was deliberate, they could take this opportunity to try for Taiwan.
https://www.breitbart.com/politics/2020/04/10/china-announces-preparation-military-struggle-taiwan/#
