The problem isn't political will per se, but specifically steamrolling local NIMBYs. The people with the most political power and will tend to push high density housing out of more desirable areas and into less desirable areas. If you wanted to, for instance, but a 100 unit building in Ukrainian Village or Wicker Park in Chicago, you'd have a really stiff fight on your hands from local property owners who want to keep their neighborhood all brownstones. OTOH, if you want to demo a square block near Garfield Park and build there--and I wouldn't recommend doing that--you'll have the local alderman holding a golden shovel for the groundbreaking.