speaking from direct experience coming from a family that builds homes in suburban southern california, it's sorta self-reinforcing and circular
people expect familiar floorplans,
planning departments approve them faster if the same elements are repeated,
HVAC, plumbing and fire mitigation regulations generally require a hub and spoke architecture
appraisers (and more importantly bank loan approvals) are based primarily on square feet, not quality (and also bathrooms)
so we add a bonus room that is likely never to be used, to bump up valuation to spend on better plumbing (developers are liable for 20 years of defects on new homes). we also build a minimum of 4 car garages, usually 6, because it's a cheap way to add square footage without added plumbing and mainly going to be used for storage anyway...
planning departments approve them faster if the same elements are repeated,
HVAC, plumbing and fire mitigation regulations generally require a hub and spoke architecture
appraisers (and more importantly bank loan approvals) are based primarily on square feet, not quality (and also bathrooms)
so we add a bonus room that is likely never to be used, to bump up valuation to spend on better plumbing (developers are liable for 20 years of defects on new homes). we also build a minimum of 4 car garages, usually 6, because it's a cheap way to add square footage without added plumbing and mainly going to be used for storage anyway...