You are mistaken. China very effectively fights against rhino horn smuggeling nowadays. It is primarily vietnam where the horn is consumed. It goes so far that the demand is heavily influenced by the economic situation in vietnam.
"Rhino horn acquisition in China is mostly reported for its investment value"
"The art and antiques market is a new threat to rhino conservation"
"Chinese rhino horn auction records (n = 7,042, 2000–2011) showed a significant positive correlation between the volume of rhino horn auctioned in China and the number of rhinos poached in South Africa"
Interesting, I had not thought of the investment market. My statement still stands though as the article also states that Vietnam is the primary consumer (at 1/15 of the population and 1/80 the GDP of China). Presumeptly China could do more against it but that would probably be a more general strategy against organized crime than against poached rhino horn especially. And of course getting rid of loop holes like declaring ivory to come from siberian mammoths or before 1990 to make them legal. China is part of Cites and that it is enforced can be seen in Fig. 3 where the auctions drop dramatically in the last four years.
Example source: https://www.savetherhino.org/rhino_info/thorny_issues/the_vi...