Ha ha - I suspect many of these foolish people are trying their luck at the casinos. Some might even be conned into investment schemes, purchase of magical stones, coaxed to donated to fake monks, etc etc etc.
You keep that flat, fully paid for and in the very worse case, rent out a room or 2 and you can expect to have a basic decent living with that $800 a month extra in rent.
Perhaps, HD can implement a 1/2 hour counselling session on why a person is selling the flat, offer suggestions, but the decison is still with the flat owner. There might be cases of children trying to take advantage of older parents with onset of dementia, etc etc THE OWNER MUST ALWAYS HAVE THE LAST SAY!
If it is a retired couple with kids all moved out, HDB could even help arrange for a purchase of a smaller room flat.