There's a strong cultural aversion in China to drugs in general (in large part due to the trauma of the Opium Wars) that need to be overcome for cannabis to be accepted, and there are signs that some progress is being made albiet very very slowly. But like you said it's indeed a contradiction that alcohol and tobacco is much more normalized. I think a lot of the heavy handed drug enforcement in China is conflated to be due to socialism, but IMO it's more due to culture and the socialist government, as any government should, conforms to the will of the majority on this issue. So the majority opinion/culture needs to shift first, kind of like the path toward legalization in Canada was in response to a similar cultural shift in its population. Am Chinese but don't live in China so this is second hand information though.