Earlier quoted context omitted.
So why haven't the protesters said this is one of their main issues?
The same reason young, social media savvy altrighters in the west dog-whistle. There's parallels in HK nativism behind these protests similar to your familiar altright talking points. A bunch of mainland immigrants "locusts" to HK to buy up real estate and perverting civilized colonial values. At the end of the day, it's a bunch of ignorant kids stewing over lost economic and social privileges and reminiscing about a…
Also, they're putting their lives and bodies on the line for this, the least we can do is extend them good faith.
If you're going to use the analogy of the west's alt-right movement, you need to explain what and who the eastern equivalent entrenched political and financial interests who would benefit from stoking protest/populism amongst the students. Without those components, you're comparing apples to badgers.