How about we bring back Sears' prefab housing?
A Sears prefab home would not be cheaper today because the inefficiencies that they solved in the early 1900s are no longer a problem. That, and it's infeasible for a person to construct their own house anymore, given building codes and such.
Cookie cutter homes can be ridiculously cheap to build if done correctly. In really large developments, it's common for teams to move from house to house every day. Almost like an assembly line. This cuts down on a tremendous amount of wasted time.
What has changed that this is no longer possible any more?
For everything else, you can do all the work yourself if you have time. I've done framing as a job so I have the experience to build a wall about as fast as any professional crew. I do my own electrical work but it takes me much longer than a real electrician (it passes intersection, though I'm more likely to need to fix something and get a second inspection). I can plan and schedule all the contractors for anything I don't want to do myself, but my inexperience means I would need to pad the schedule a lot more than a general contractor (and the fact that I'm not a regular customer means I'm not top of their list to get my job done)
Each city and sometimes inspectors have their own codes. Sometimes they are good things (going beyond the basic codes), sometimes the inspector is just making things to enforce even though there is no engineering reason for that.
There is no reason you can't build your own house (except plumbing). However it will take a lot of effort. Professionals are up on all the codes and the latest tricks and so will be a lot faster.
Why not have a backflow preventer at the mains and call it a day? I get electricians in a way, but plumbing... eh.
Insert the George Carlin quote about clubs here...
"Professionals" also get preferential treatment from municipal governments. I'm pretty sure the only thing my local building inspector did was sign paperwork - good thing I found an actual home inspector that had a construction background because he found electrical, plumbing and framing issues so glaring it's obvious the local building inspectors "inspected" from the curb only :p
My parents built the house I grew up in and over the years I've helped several friends build their own houses and the amount of trivial crap they had to put up from drunk on power building inspectors is nuts by comparison. It's an utter farce. The problem is very few people will ever experience it, so it's easy to not even realize what's going on.
Until a large condo suddenly collapses in the middle of the night :p
That said, my experience with inspectors is they know who are the good ones and who are the bad ones. The bad ones get everything looked over closely. The good ones get a close look once in a while, but if the inspector is busy a quick look is all they will get. Trust comes from the inspectors experience in this case though, something that one off homeowners obviously haven't earned.
You can do a large chunk of the work yourself (with a crew). But utility hookups are a no-no without a license. And you'll probably need to hire a crane operator at some point. Plus, there are a ton of building codes in regions that are different from other regions. So you'd better get those all right unless you enjoy rework.
Also, something many of us are forgetting about: value of house is mostly not a structure. Having this house on 1/8 acre lot in the middle of desert would be horrible. You need water, sewer, power, internet, grocery stores, farms, parks, hospitals, gyms, coffee shops, theaters, airports. Structure alone wouldn't provide for this. It's the access to all the infrastructure that makes home so valuable