It's odd that its like that - assembly line production doesn't have to equate to poor quality, and with the things I own its
usually quite the opposite. Done right you can have good materials made into complicated things cheaply. However I'm yet to see (in the flesh) a prefab building that I like. Grand Designs, the UK show, has shown a few great ones featured but its a shame there aren't more to be seen as making a house on a production line would solve many of the things home owners grapple with. In the last month alone I have replaced a shonky toilet, a leaking pipe from bad install, bad fuse box case, several bad roof tiles, weird sink plumbing and 3 cheap crappy doors. If production line assembly can make these jobs easier and more standardised (how many different diameter pipes can one toilet use!) without resorting to cheap junk that whilst creating houses that look nice, I'll be happy.
Prefab house sounds like the big builders. Everything that can be installed is the cheapest garbage that can legally be sold. If you watch big box home retailers (home depot, etc) they even make fun of it by calling the worst possible model they sell the "contractors special" or "builders special" to emphasize that no one who intends to live there and be stuck using it, would ever install such garbage.