they can assemble houses on sight that fast too. however it is a lot of management and you often have people standing around waiting until someone else finishes their part so they can start. . it is done as a stunt once in a while, but for price reasons it takes a few months.
https://youtu.be/kqn1BBudPS4
There’s bound to be companies out there that do the same with houses. I think the Scandinavians are meant to have quite a lot of flat pack housing.