They have a bunch of issues, and the only thing that is really automated about them is the walls. Since it's basically unreinforced concrete they have a horrible time with insulation, cracking, delamination, and shrinkage. Not to mention that they aren't very good at producing sharp or square angles, so a lot of your door and window work is custom or done manually.

If you know anything about residential construction, building the interior and exterior walls is not exactly an especially time consuming or expensive part of the build process. A decent sized team of good manual workers can put up the exterior and interior walls of a decent sized home in a week or two. The 3d house people say they can do it in 72 hours of machine time.....which can run anywhere from 2 weeks to 5 months in real time.

you cpuld have a factory that cranks out walls and some sort of automated system that assembles them on site.

That idea is over a hundred years old. I currently live in a house that someone bought from a sears catalog in the 1930s. They would flat pack an entire house and ship it to you on a train for you to put together yourself, or you could hire a local sears approved contractor that had a team put it together for you.

IIRC “3D Printed” houses are falling apart due to lamination issues. That said, I think it's a solvable problem, though it will take awhile to sort out the issues. Modular systems also show a lot of promise for mass production, potentially even of higher quality, and likely amenable to robotic assembly if carefully designed for it, but we know it'll just be a profit seeking race to the bottom. Those construction jobs are safe for at least a decade, likely more.