Because China Gov owns around 200,000 btc and this is a lot. More than US government. By reasoning, their voice is bigger compared to US government in cryptocurrency.
Should we take china words seriously? No. Because they been trying to ban since year 2013. Then they un-ban and then they ban again. History repeats.
To clarify the Chinese government itself does not own that amount of btc, that is the amount of bitcoin that is mined or owned by Chinese people or companies or at least used to, and they ban bitcoin and crypto not because they are trying to create some reversal strategy where they ban it and than unban it to pump its price, at least it does not seem so, they did so because of how freedom is restricted and restrained by the government on its people, it is a well know issue where we all know that they have created their own version of everything so they don't have any outside influence, and because of how bitcoin and crypto gotten so big over the past years and how they are unable to control it they have banned its use, and i am pretty sure they are working on making their own crypto that they will make their citizens use it, just to use some more information gathering and control on them.