A key difference to understand between protests in America and in Hong Kong is that there is no division in Hong Kong about the issue. In the US, for example, half of the population opposes Trump and half supports him. There are anti-Trump protests and pro-Trump rally. The US is divided on many issues.
In Hong Kong, the whole population is united against the government. The territory is democratic on paper, but no longer in practice and basically run by the CCP.
(Note, recently moved from the US to HK and went to see the protests for myself yesterday, though I didn't actively participate)