I am curious about your presumption that pre-fab construction “has a massive reduction in cost”. Anecdotal evidence suggests this allows for faster construction on site (as you say) but hardly any costs reduction. From what I gather, the pre-fab units are still constructed uniquely with manual labour, only in a factory hall instead of on site. Extra transportation efforts seem to destroy most of any cost savings. The actual massive line production of standardized units ready for construction does not seem to exist anywhere for house construction, as it exists for other manufacturing. Happy to be proven wrong and learn more though!