Well, Carrie Lam the current chief executive of HKG, has a notorious nickname - Habitual liar.
She's been caught breaking promises again and again and cheating her way out of difficult situations in the past. That's why many people do not trust her.
Well, politicians and people cheat all the time, but when you keep cheating publicly without remorse, it's gonna bite you back, hard. And that's what's happening now.
FWIW, she's said during in one of the election forums, that she would resign if the majority of HK people think she's not fit for the office. Her rating stands at 27.9 points in the last survey.
Of course, there are other things at play here, specifically, CCP/Xi is not willing to let her go for now.
Hope this can give people some perspective on this issue.