> People in developing countries (most of the English speaking internet) overestimate the efficiency of the Chinese government.

I disagree. I suspect that people in the developing countries have quite a clear view of just how brutally efficient the Chinese government can be if it wants to be.

You don't just magically create industrial quantities of a banned gas without having a market for it. As there is no other market for this besides inside China, these producers likely got at least tacit approval/gave solid bribes from/to important folks in the party.

If the Chinese government wants this gone, it will disappear. If it doesn't disappear, the Chinese government doesn't really want it gone that badly.