If the land is appreciating at 10%/year then it is a no brainer to borrow against it at 4% (pre tax)
This was a point in a presentation about issues in local urban communities I attended a couple years ago. (The dynamic is not great for a community.)
In general the non-use is not very widespread, and partly thanks to 唐樓 architecture there are plenty active small businesses in residential areas (I haven’t seen such abundance while staying in mainland cities). I believe the reason I saw it come up is the existence of active and conscious members of the community who are more invested in its future and sensitive to upcoming issues.