The only reason these protesters have not simply been shot with real bullets is that China can't afford the massive negative economic consequences that would follow, as people would become afraid that China has become authoritarian enough to just nationalize everything within their reach, including all investments anyone may have made into China. Government-based tariffs are bad for them, but within the normal domain of country's relationships with each other, and can be managed as a known risk. The entire world just deciding not to do business with China would be catastrophic for them; they can't just hope a particular politician gets removed or that they might be able to offer enough concessions to get tariffs removed, they would have no recourse.

Non-China ("Western" doesn't quite cover it, there are others too) economic interests are the only things keeping these protesters alive.