Finland is a model of 1) good land use policy (Anna Haila's study of Singapore is also fantastic for understanding this), 2) excellent efficiency of organization and design in social housing (they run competitions and stamp out winning designs many times, getting economies of scale), and 3) understanding market economies and using the buying power of a large builder to be ruthlessly efficient in construction, 4) somewhat sane permitting processes and allocation of resources to social housing builds.
4 and to a lesser extent 3 above are the biggest differences with the non-profits that build below-market-rate housing in California. In California, the non-profits must fight like hell to get any permission to build, and that process can easily take years upon years, with uncertain delays along the entire process. In the meantime, funds that might go to the project will have deadlines on them, and any project will actually be assembled from a large and diverse set of sources that vary from grants, to loans, to LIHTC tax credits. And for the funding that comes from an application process to other organizations.
All this means that the entire build must be 100% subservient to the needs of getting local build approval and funding gathered all at the same time. Any project that focuses on minimizing costs is going to fail because the other parts are so hard to pull together.
IMHO there should be changes to local approval such that when plans are submitted, the city has 90 days to give final approval or rejection, with zero, absolutely zero extensions. And if the city rejects projects that follow the rules, or takes longer than 90 days, then that city loses any control over permitting for a year and a disinterested state board takes over, with the city paying the state for that cost.