Since you mentioned those places, how many crashes into local built up areas do you know of at Kai Tak and London City? Not a lot......in fact zero. Simultaneous engine failures in a twin are exceedingly rare. You do not have many options. It would be nice to have plowed fields around airports for the incredibly rare events should they occur, but the trouble is when you build an airfield out in the wild blue yonder,
1- people don't want to travel so far to a local airport for a short twin type journey, and
2- once the airport is working, people want to live nearby, so they build houses, and schools, and Tescos, and Income Revenue offices, and before you know it
3- there is a local noise group complaining about noise and safety in the event of twins going off the runway.......