China could be calculating the upcoming U.S. election into the timing of enforcing crackdowns on the Hong Kong Protestors. The situations in the United States is that the U.S. Citizens are very much aware of the situation in Hong Kong to some degree, especially the waving of the United States Flag and statements by some Hong Kong protesters expressing support for their own version of the Second Amendment. These immages coincided with a mass shooting in the United States, and were used by the Pro-Second Amendment side of American Politics to push back against calls for more restrictions on the right (many pro-second amendment Americans believe that it is a check on the very government pressure that is feared will happen in Hong Kong).
These groups tend to be largely supportive of Donald Trump, who as mentioned, is currently negotiating trade terms, and while he's very clearly critical of China (going so far as to suggest American Companies leave China, which many either already have or are currently working on doing), he'd much rather get a favorable deal then leave the table over a riot. Of course, this has lead to criticism of Trump for not responding to the situation in Hong Kong from his opposition.
Economically, the United States is a bigger player in the world markets than China. If either party walks away from the Trade War without a deal, they both suffer economic down turns, but the United States economy is such a beast that it can weather that storm better than the Chinese economy, which relies on the United States basing much of it's manufacturing jobs there. While Trump may be at the table to negotiate with China despite China having a very public uprising that it feels it needs to get control on, political pressure on a U.S. President in a re-election cycle might force Trump to walk away from the table if China makes an aggressive move on Hong Kong. Not only are his supporters loyal, even to a fault, it will play well with his opposition, who are more concerned about the civil rights of Hong Kong citizens than trade negotiations with China.
Losing the U.S. Market and Hong Kong at the same time is going to be a nightmare for China's economy. Most of the people who do trade with China also do trade with the U.S. and if the United States says "you either trade with us, or you trade with China", most of those countries will side with the United States.
The power of the Chinese economy is the sheer size of it's population, not it's policies. To give you an idea, in a GDP(PPP) comparison, China is the largest overall economy and the United States follows behind it, just barely. But when adjusted for Per Capita (population), The United States is one of the top 10 GDPs in the world, while China drops to somewhere between 72nd and 83rd most powerful economy in the world. And in case you were wondering, the nations with a higher GDP(PPP) per capita that are higher than the United States, are mostly tax havens and are have a much lower population than the United States (3rd in the World).
This means that for any equal amount of population, the United States Economy is much more powerful than the Chinese economy, and China is only the most powerful because it's got way more people than the United States (a billion to 300 million, 3rd by population). It's worth noting that India is the third largest Economy overall and second only to China in population (but is low on the list in GDP(PPP) per capita).
And why does losing Hong Kong hurt China? Well, if we did a GDP (PPP) per Capita of Hong Kong, we find that it's slightly higher than the United States economy. So really, if China is going to have problems with the Hong Kong protests and the United States walks away from Trade Deals over China's handling of Hong Kong, they are risking alienating two economies that are the strength of the United States in the same go. And unfortunately for China, the next largest economic zone it has domestic access to is Macau... which has a GDP(PPP) per Capita just south of the combined figures of the United States and Hong Kong... and is also a Special Administrative Region (SAR) like Hong Kong. So really, China is risking alienating three economies, all of which have a hand in China's role in it's number one overall economic strength rating. And India and China are not the greatest economic partners... and can largely fill the same low skilled job needs china can for the U.S. as can just about any nation in the general area.
The one thing working in China's favor is that it's government will not be changing leadership in the near future as opposed to the United States, which is about a year out from getting rid of a leader who is "Hard on China" and installing an unknown leader in his his place. If China can not act on the Hong Kong situation for a year, the chances that the possible "Not Trump" leader also being "soft on China" is a lot greater then if they immediately move on Hong Kong, which will likely cause the current leader to walk away and the unknown candidate running against him to adopt a stricter policy on Chinese relations then if they didn't act. They can play the waiting game on both Hong Kong and the United States at this stage. What is one political year to a President for Life?
Diplomatically, it also looks bad for China as the Hong Kong SAR status is part of a treaty it negotiated with Britain and while Treaty's are only enforceable as long as all signatories agree to enforce their ends, China not honoring the right of Hong Kongers to protest means China is breaking it's end of the treaty... As mentioned that Belt and Road program of China's relies on China being creadible to hold up it's end of the bargin with a lot of other countries. If China is acting like Darth Vader and "altering the deal" with one country it had a deal with, the other countries considering China's Belt and Road program might pass as it's always better to not make a deal then to "Pray it's not altered further." After all, it was China that introduce the concept of "Fool me once, shame on you, fool me twice shame on me" to the world. And China isn't playing nice to countries it offers the Belt and Road program to just because they feel generous... they benefit by getting access to things they need, namely oil which is bringing electricity to a billion plus people living in China.
So from the Chinese point of view, immediate action means risking the brunt of major economic down turn, a possible energy crisis, a popular uprising in an SAR, a possible second uprising in another SAR, an unemployment crisis of a large magnitude, in a culture who traditionally believe that their rulers are subject to Divine Mandate (that when the country is suffering, it's because the gods are not happy with the leadership and revoked the mandate given to the leader to lead... and the disasters are the god's way of telling the people it's time to find a new government.). But if they wait a year or two the protests will likely die down or the international powers will shift in a way that China can better respond too. Right now, it's better to wait for a change in the situation where the government isn't being eyed so much by the international stage. They'll have a better idea of what to do in response once a couple of other situations with deadlines resolve.