Because a large portion of the important and high-value stuff is not actually made in China, is is just assembled there. Your iPhone might be "made in China", but most of the parts that make it an iPhone are made in other countries. If you were to consider the things that we think of as being essential then the fraction of things that are made in China becomes even smaller. Yes, we would need to do without cheap bras and Levis for a short while, and the strategic plastic shit stockpile would dwindle, but the nation would somehow get through these dark days.
China, OTOH, would likely never recover from having all of its revenue generating export goods evaporate to other countries in SE Asia and elsewhere.
China, OTOH, would likely never recover from having all of its revenue generating export goods evaporate to other countries in SE Asia and elsewhere.