This answer was contributed by a friend, Dave P, who has expertise in green buildings:
Hmmm...well the short answer is cost. Budgets for building low-income housing dropped drastically under Nixon and even further under Reagan and never really recovered. The system innovated under Nixon (which essentially killed public housing as we previously knew it) was the community block grant system. The federal government decided it would no longer fund public housing directly -- it would give municipalities and states "block grants" which could be spent on a variety of projects. Those state and local governments could build housing with that money or do other things with it. And we more or less have that system in place today.
But the main point is that the money coming into any given city is very low and local governments (to the degree that they care about low income housing at all) will usually opt to build more units the cheap and dirty way rather using building materials that are renewable. (Less cost per unit = more units = less homeless people, etc.) Sometimes the cost of using sustainable building materials can be offset by federal, state or local subsidies but usually such programs will focus on energy efficiency (insulation, efficient heating and cooling systems, appliances and fixtures) rather than renewable flooring materials.
However, to me this question opens up larger questions about low-income housing and sustainable building materials...
