But the Central Committee isn't really an independent body, and the people who sit there are selected by the Politburo - effectively the Politburo members just vote themselves in.
(P.s. as mentioned I'm not 100% across the politics in China so happy to be corrected)
[1] https://en.wikipedia.org/wiki/Politburo_Standing_Committee_o...
[2] https://en.wikipedia.org/wiki/Central_Committee_of_the_Commu...