No conspiracy, it actually pretty simple, not enough of the population, especially over 60s have had 3 shots, which according to studies 3x shots of the China vac gives 97% effectiveness. China's health system simply cannot cope if they removed lockdowns, millions would die, the health system would collapse it no time and would be a complete disaster. Less than 70% of over 60s have more than 2 shots and that was years ago.
The solution would be to mass vac the entire population on a very regular basis or use the Western ones (which they will never do) but I'm assuming the logistics are very difficult and costly because if they could they surely would as their current approach is a horrible existence.