The main reason 'housing' is getting more expensive is zoning regulations + limited supply of land in desirable areas. You can still find cheap houses in places that not many people want to live in.

Someone tried to do this in Boston by hiring Maine residents to build the components and then shipping the components down to be put in place. The permit was rejected in part because it was taking away local jobs and in part because it would change the character of the neighborhood.

The value of homes is mostly in the land. 600k house? the land is 350k, construction materials and labor comes in at 150-200, 50-100k left over is margin for the developer.

Yeah. Does anybody know why walls for houses aren't built in factories (with electrical, plumbing, insulation, etc already inside)?

Yes! From first principles, one look at materials cost to build a home leaves one with the feeling that prices could potentially be cut by an order of magnitude.