It's hard to take drastic actions in times of peace. Once the shooting starts and people are being killed, there is a much higher chance of the US overreacting than underreaction, and the actions put into place against China (military and non-military) will likely be very tough.

e.g. if China actually invades TW and people are killed, the US has both military options and non-military ones like USD cutoff, blockade of critical Chinese imports of oil and food, even repudiation of UST holdings, etc.

China can't ignore these possibilities once the bullets (or missiles) start flying, and how emotionally charged things will get (and the possibility that failure is high and fatal)