I also think seeing the US police response to the BLM protests/riots in the US took a lot of the wind out of HK protestors' sails. The BLM protests were so widely promoted and publicized in China (so CCP can say, look at the chaos and civil unrest in the US). But rightfully it highlighted how relatively reserved HK police had actually been relative to some US cities' militarized police response, arresting journalists on camera, shooting people in the face with rubber bullets, outright beating protesters etc.

I think it made some HKers realize maybe things are not so bad, that actually police brutality against protests/riots can occur in democracies too...