Most HK local people bought houses when the price is low. The average income is around $20k. Those people have several choices. One is to live with parents. another choice to is rent place less around 400 sq in new territories. most of them alreayd bought tiny places when they got married.
Just like in Mainland, most local people already have place to live. Parents could help them buy one place when they got married.
So the high rent price mostly hurts the people who relocate to HK.