For a small house, we (two of us) might spend a week and a half installing the hardwood floor, doors, baseboard, window trim, crown moulding, closet shelving, stair trim, etc. as well as the inevitable custom bit of this and that that always takes forever because they weren't accounted for in the drawings or a prior trade screwed something up (we don't do stairs, railings, or cabinetry; those are all done by other specialist tradespeople). For a large custom house, we might be there for a month.

Now multiply that by every step of the process: excavation, foundation, concrete floors, framing, exterior windows and doors, roofing, wiring, water and waste plumbing, HVAC ducting, gas plumbing, back-framing, drywall, taping, floor installation, tile work, trim, kitchen installation, stair installation, back-trim, painting, plumbing and electrical again, exterior siding and/or masonry, landscaping, connections to city services, paving, overhead garage door installation, and so on. That's a lot of people doing a lot of highly-specialised work, and structural framing is a tiny part of it.

So yeah, I'm not building my own house anytime soon. I'd sooner do a live-in renovation because those tend to be much more limited in scope. And there won't be a single breakthrough that makes building houses cheaper, because the work is by necessity highly variable and dependent on geography and local factors.