Many rebellions, uprisings and revolts have been started by "Incels", the most recent one being the rise in white nationalism in the west due to many, disenfranchised low quality white males who are still unable to succeed despite being the privileged demographic in an age of OnlyFans and #MeToo preventing them from getting sex.
Previous revolts have also included the arab spring and the rise of Islamic State, from the jobless, youths who either fled to europe to commit "Ta Harrush" or decided to try their luck with Yazidi sex slaves.
There's really no motivation for young men beyond sex and the desire to dominate; in a healthy society, this is channeled into sports and sales jobs and pro-social avenues like entrepreneurship. In unhealthy societies, you either get Otakus gaming their life away or Islamic State.
Looking at the HK perpetrators, you even had white collar workers amongst their ranks so i'm inclined to believe sex, or lack thereof was a factor, especially in a city as white worshipping as former British colony HK. Chances are HK women would have on the whole, deigned to go for "white romantic anglo male" as their indoctrination dictated, leaving the inevitable Incels, ripe for anglo demagoguery and manipulation.
Hong Kong is a place which has very materialistic girls as you would expect in any big expensive city.
Yet unlike most other big cities, it has no hinterland where costs and female expectations are more reasonable.
Hong Kong is also similar to most countries where females significantly outnumber males in higher education, and presumably in higher-paid job opportunities. It also sets the bar higher in terms of what is an eligible man in terms of education and wages, particularly given property prices in Hong Kong.
So that leaves lots of unmarried higher-educated women and unmarried lower-educated men.