Not only that, but prefab on a literal factory production line can do a far more consistent job of what finishing is possible pre-assembly than you can do on-si

Not only that, but prefab on a literal factory production line can do a far more consistent job of what finishing is possible pre-assembly than you can do on-site. Yes, construction workers are good at this stuff, but they're unlikely to compete with TPS-style production line optimisation on cost or repeatability. You can't even use rapid fabrication to set the plant up at the point of need, because wastage in the construction process means that it takes less energy to ship the finished product than the component parts you'd need in your supply lines.