While that's a possibility, it not necessarily the route they're taking. As the link I pointed out mentioned, there's potential benefits from mass production as opposed to constructing singularly. I see key benefits coming from:

1) Logistics. While the finished products still need to be taken to site, not all sites are convenient for materials or close to suppliers. Good placement of factories can have time and cost savings on sourcing raw materials.

2) Expertise and specialisation. When you're using a factory to produce many thousands of homes quickly you'll be able to break down the skills and focus on each individual aspect.

3) Targeted employment. If factories are placed in areas with declining industries it can be used to revitalise local economies who need it most.

And, like the article I linked to says, the major benefit to building inside is being weather proof. A lot of construction work is a no-go if it's too wet or windy. Bad weather can and does delay construction. Factory building negates that.