The answer to your question is very simple: It is because our national-level leaders have no earthly idea about what they are doing. Housing is a predominately local issue. It is ordinarily constrained by local policies. These constraints include zoning, housing codes, and building codes. Of course, there are a few national level issues like inflation which largely impacts interest rates on such instruments as mortgages. It could be that in any given country building codes are national, but local governmental bodies like to mess with building codes too.

This is an answer that comes from someone that has not been in South Africa, but has worked in spatial planning (regional and local) in many geographies. I agree with Mr Colwell in the fact that in most countries housing is clearly influenced by local governments through land use planning. But it is also true that in some countries there have been national level policies that promoted the creation of affordable housing or of social housing (the degree of public involvement makes the difference), which can become a substantial share of the housing stock (see the case of some European countries, and especially the hardest hit during ww2). So, if your national leaders have that in mind, this could be a reason. But this means allocating substantial economic ressources to that end, and a clear political consensus to ensure a consistency of such policies over the years. See for instance the case of Hong Kong, where the British promoted public housing policies, with what in Europe would seem low standards, but so got some degree of control over the pressure of migration from the mainland. This, in the end, leads to the debate on the role the state can play effectively in providing basic goods as housing, especially in societies with substantial inequality, and it is far from a closed debate.

Housing is never a pure economic issue. It is always a social and political issue. That is one reason why many national governments get involved in housing. In China we have housing planning although I don't know how effective it is.

Good housing and process of overall socio-economic development remain positively linked. In addition to providing, security, safety and raising the quality of life, housing generates and creates supportive conditions which are considered human centric

Housing is among the drivers of economic growth. It is a basic human need for social and economic development. Investment in housing contributes directly and indirectly to capital formation; employment creation; income generation; increased savings; improved health; and increased labour productivity. The result of which is economic growth and poverty reduction. Recognizing the inseparability of housing and social economic development, and in order to give the housing agenda the attention it deserves, this housing policy is formulated to serve as a comprehensive framework for guiding the housing sub-sector.

Housing investment contributes to reduction of poverty through creation of jobs during planning, design and construction of houses, provision of infrastructure and services that go with housing development. Also jobs and other income generating activities are created during the process of building materials production and supply. There are also employment opportunities resulting from the processes of financing, selling, renting and maintenance of houses. Other employment and income opportunities are created from indirectly related activities. In this regard, housing development has a potential to contribute significantly to the economy and physical wealth of the country. Housing is a significant part of wealth and the fixed capital stock in an economy.

Source: Draft National Housing Policy (2018), Ministry of Lands, Housing nd Human Settlements Development, Tanzania