Because a machine is expected to do it right the first time. Because it's supposed to do the exact same thing everytime with the exact same input parameters. If you give it the exact same input every time and you get a different result every time it is not reliable to function as automation.
Humans are just that. Humans. They make mistakes sometimes. The reason humans can keep doing the work is that there is no better alternative. Machines can't do it, so who else is gonna do it? Either humans build your house or nobody does. There is little choice there.
So if a machine is to take over that job, it better do it right and reliable and cheaper.Because humans can already do it right and reliable. And there's little money saving if a human still needs to check all the work.
I've heard most of the shops sell the same matrassen, but they just give them different names so you cannot compare prices. Which means you can make prices anything you want as long as you have a somewhat believable story about the quality.