It doesn't seem difficult at all to me.

First of all, the target is not 'below the maintenance cost of the human body'.

The target is 'below the minimum wage that we can pay a human to work for', and that is a very different metric.

Also, as for uptime... The average human performs work at roughly 60% duty cycle. (8 hours sleep, plus meals, bathroom breaks, etc). That is a pitiful number compared to robotics.

Also, when you pay humans at bottom-of-the-barrel prices, they don't have high morale. They are rude to customers. They steal from their employer if they can get away with it. None of these apply to robots.