It was a British colony, ruled partly by increasingly-elected councils and executives, including the Governor, appointed by London (not the monarch, except in name) with consultation with the locals. The last time the Hong Kongese rioted against the British was in 1967 [2].
There isn’t a comparison between British Hong Kong circa 1990 and the present iron grip Beijing holds over it; freedom of speech, for instance, prevailed as did the rule of law. There is much less comparison one can make between free Hong Kong after 1997 and the mess Xi has turned it into today.
From TFA, also 1981, 1982, and 1984. (Admittedly, these were generally economics-driven)
>> After the [1967] riots, the British Hong Kong government publicly reflected on its failure to address certain social grievances and carried out major social reforms. However, another series of riots would occur in 1981.
Given that the 1967 riots were explicitly CCP-supported, they've a clearer line to regime change as a goal.
And given the CCP was somewhat busy in the late 70s and early 80s rendering Mao's excesses anathema [0], it's unlikely they saw formenting revolution in Hong Kong as a priority.
[0] https://en.m.wikipedia.org/wiki/Chinese_economic_reform#1979...
[1]https://en.wikipedia.org/wiki/Governor_of_Hong_Kong