Who then is to blame? Well, let's avoid blame games, and try to understand instead. I think the relevant history is the introduction of Town and Country Planning Acts in the late 1940s and the process which led to leasehold reforms in the 1960s, which gave leaseholders to right to buy out their freeholds on attractive terms. As a consequence, the Thorpes Estate, where I believe the Pru was the freeholder, is now largely owner-occupied, with isolated social housing mixed in. The leases would have expired around 2000, 99 years after the original development, at which point the Pru, but for leasehold reform, and modern planning policies, could have looked at the area, including I suspect the shops on the north side of Sydenham Road, and invested as they thought best, although necessarily taking account of where they saw demand for new retail and housing. There's an interesting footnote to this history, in that (I believe) the ultimate successor to the original freehold, from which all other property rights have been carved out, has now only the residual liability to maintain the unadopted 'Earlsthorpe Mews' (a.k.a Sydenham Mews) in good condition, and so has become rather difficult to track down.
I found another - rather tenuous - Sydenham connection when researching this, in a son of Ernest Shackleton speaking in a House of Lords debate in 1967 arguing for leasehold reform. Helpfully he began by explaining how the previous system worked:
This is a difficult and complicated subject with which we are dealing this afternoon, and it is no good believing that there are necessarily simple solutions. The leasehold system—that is, the leasing of land for a long term of years for building—is peculiar to England and Wales. So far as is known, it does not obtain anywhere else. In Scotland, of course, a kind of feudal tenure still exists in which owners of land owe feu duties to a superior, but that is not quite the same thing as leasehold tenure. The essentials of the leasehold system are that the freehold owner agrees to let his land at a ground rent for a term of years, 14 usually a long term, 99 years or even longer, to a builder or developer who is required by the terms of the lease to put buildings on the land to the satisfaction of the owner. It was under this system that the eighteenth century saw the development of what are now regarded as some of the more elegant parts of our towns—the Cadogan and Grosvenor Estate, Bloomsbury and so on. The merit of the system was that the landlord could ensure control of what was built on the land and of the upkeep of the estate once it was built. He did this by means of the leasehold covenants. Before the days of Town and Country Planning Acts, the leasehold system was, in effect, the only means of securing well-planned and well-maintained urban development, and of securing that estates could be redeveloped in an orderly fashion as the buildings fell into decay.
Of course he then went on to explain why leasehold should have been reformed, which I would say was largely because of the ill effects of the end of lease period, when leaseholders no longer had an interest in maintaining their properties, and freeholders would allow an area to decline in anticipation of a chance to clear out existing tenants and redevelop an area as they saw fit. At the time I think the reputation of Peter Rachman cast a shadow over the role of private sector investment in housing - and it probably still does, even if the name of Rachman is now largely forgotten.
As well as the discussion about Earlsthorpe Mews already linked to, this is relevant to these other threads:
Building to let
The solution for High Streets like Sydenham
Let's all drive vintage cars!
"so people build c--p.”
Does FH Soc want more affordable houses?
and any number of others I have contributed to on housing and local civic societies.
As to where I'm going with this thread - mainly trying to find out and understand more, and see what empirical evidence there it to support / contradict my argument, in the first place to quantify what fragmentation of freeholding there has been - if any. Of course, it would probably amount to doing a PhD covering economics, town planning and the relevant political history, and I don't have time for that, even if I could. OTOH, someone else might have, and I'm interested to find out more.