That's the really annoying thing: there's no really good reason cities can't build more decent housing in high-rises. I suspect the problem is bad zoning laws and developers able to make more profit doing other things. Ideally, cities should be able to get developers to build lots of high-rises with moderately-priced condos and apartments, to pack more people in, which would also increase the efficiency of public transit. And these units should have a decent amount of space, by building up, so families can have a reasonable amount of living space. They just need to take action to clear out older, smaller buildings taking up valuable space (probably with punitive property taxes), and encourage development of high-rises (with property taxes which punish buildings that are too small).