China seems to be facing the dilemma that they either lose the digital currency race against the USD (also due to the dominance of USD-denominated stablecoins) or would have to allow CNY-denominated stablecoins [1].
For now, they
chose not to change their policies. Even if one can say that with the growth mentioned in the OP in mind, their policy of "tight control" has likely failed. The e-CNY also struggles with adoption.
On the other hand, I've read elsewhere that the Chinese government probably doesn't care about the USD stablecoin growth as long as it stays relatively small, i.e. as long as stablecoins are used only by a minority of Chinese citizens. And that the more open regulation in Hong Kong could be a pilot project to reconsider the "de facto crypto ban".
[1] There are some CNY-denominated stablecoins, but they are not issued by Chinese entities, no license has been given to them even under Hong Kong law. The only CNY stablecoins are small and from foreign companies, Tether discontinued its CNY stablecoin this year due to low demand.