The lack of building comes from the bad zoning laws preventing builds. The rules at the local level are mostly favourable to existing owners, who by a large margin, want their existing property and environment to remain as static as possible to what they purchased (ala, the character of their neighbourhood).
And not to mention that even if they, in principle, agree with denser housing, they would face problems with crowded infrastructure that has to be paid for (and mostly hasnt been upgraded or improved, like public transport, road conditions, grid connections etc).
Therefore, the best current option is to push the affordable (read: high density) housing away from where you are, even if you, in principle, don't disagree with the ideals of it.