They don't. It's already illegal there.
Factories creating that gas are doing so in secret and are unregistered.
Licensed factories secretly using that gas appear to be good at evading the discovery of that fact by authorities, partly due to corrupt inspectors.
It's mentioned in the video in the linked article.
If the oceans rise 2 meters half of their coastal citys are in for severe flooding.
But the same could be said for any hyper capitalistic society without rule of law or strong regulatory enforcement. That just happens to mainly be China right now, but could also be the USA in the future if the EPA is dismantled and Trumpism reigns.