Might also be they're very aware of how fast it can spread through their population, the demographic of their population, and the sort of conditions in which their population live and work, and how it could utterly mess up their health system and their economy if left uncontrolled.
People may be upset about how strict the rules are now, but that's probably nothing compared to how upset they'll be if large numbers of their family and friends die because it's just allowed to rip through the population, and it likely would given how crowded the big chinese cities are.
They'll also be very aware that their vaccine is less effective than the western ones (from memory), and that they've had a fraction of the uptake for the boosters etc compared to the west and seen how our numbers are and how our policies have led to a lot of continuing disruption.