Precisely because it has been so successful with its "dynamic zero policy", China now becomes vulnerable. There is a large group of vulnerable people kept alive by that policy and they may now be exposed to Omicron. Most of the same group in the West are already dead-- killed by Covid.
Hope that some effective anti-Covid drug will become available soon. Otherewise, China might have to make a very difficult choice between opening up and the lives of these group of vulnerable people.