In the old days it was common to build your own house. And it usually allows a house for half or less the market price. But this is effectively illegal/impractical in most the US. Some simple changes to legislation would halve the average cost of a house overnight!
Since the house was built without any compensation and not used for any commercial purpose, it bypasses "commerce" which was the auspice under which housing was regulated. When I was done I literally just sent the county a picture of a house and they closed the permit and that was that.
And it wouldn't be just the currently-active NIMBY's who fought tooth and nail against any "simple changes" that might halve the average cost of a house overnight.
But you can't, because the lot is unaffordable
edit: as a comment, there are a lot of people in places like big island hawaii for instance, that do something like this under burner LLCs with shipping containers, then just move them when caught and do the same thing over again.
Some people have valid excuses, but most do not.