A surprisingly clear report from California noted much the same:
“Many housing programs — vouchers, rent control and inclusionary housing — attempt to make housing more affordable without increasing the overall supply,” the report said. “This approach does very little to address the underlying cause of California’s high housing costs: a housing shortage.”
So, why does this happen? Reason blames self interested home owners, renters in rent-controlled apartments, and the politicians who kowtow to them at the expense of largely poor people who cannot get subsidies and would-be homeowners:
Homeowners have a strong economic incentive to restrict supply because it supports price appreciation of their own homes. It’s understandable. Many of them have put the bulk of their net worth into their homes and they don’t want to lose that. So they engage in NIMBYism under the name of preservationism or environmentalism, even though denying in-fill development here creates pressures for sprawl elsewhere. They do this through hundreds of politically powerful neighborhood groups throughout San Francisco like the Telegraph Hill Dwellers.
Then the rent-controlled tenants care far more about eviction protections than increasing supply. That’s because their most vulnerable constituents are paying rents that are so far below market-rate, that only an ungodly amount of construction could possibly help them. Plus, that construction wouldn’t happen fast enough — especially for elderly tenants.