It’s generally speaking not cheaper to refurbish something once you consider all of the factors. I’m on mobile so I can’t enumerate those but I’ll try to return on desktop where I can properly type and give an overview.
If you don't mind my asking, what is your main hustle?
The point is satisficing vs optimizing. An old house or apartment is already livable, in a supermajority of cases. It "needs" nothing, in the strictest sense of the word, and putting it through capital repairs will very likely put it in the red, possibly even compared to building a new house.
Sure, some repairs and improvements may be useful. A universal coat of paint is probably the lowest hanging fruit, mostly due to the broken window effect, and especially if it includes common spaces. Very cheap credits for stuff that will definitely pay itself in a few years, like thermal insulation or heat pumps, depending on climate. Regular checks to make sure it passes very very low safety standards. And that's about it.
Instead of actual brick and mortar?
We use spray foam insulation and good materials for flooring and trim that won’t wear out tomorrow.
We build for about the same as it would cost to take an existing house; demo out all the stuff that doesn’t meet code, make it meet code, then put back all the good materials that won’t wear out tomorrow.
Trust me your big line items are still there when you refurbish something to meet codes; and governments aren’t going to fund projects that don’t meet code. That is before you even get to the discussion of what people actually want their finishes to be.
I suppose the levels of grandfathering of old rules varies from place to place, no? Though for public financing I guess they want less "old" stuff?