Given some candidates will be denied without interview, one possible explanation is your candidacy is not strong enough to warrant an interview initiated by the admissions office.
Take a look at your essays along with your GPA, G/T scores, and you may find if the whole application has some areas for improvement.
I don't think the score of GMAT or GPA is the key issue. I suggest you double check your application material whether to meet the requirement of HKUST. You'd better find a experienced person to help you review your applicaiton.