I think that’s generally because humans can be held accountable, but automated systems can not. We hold automated systems to a higher standard because there are no consequences for the system if it fails, beyond being shut off. On the other hand, there’s a genuine multitude of ways that a human can be held accountable, from stern admonishment to capital punishment.
I’m a broken record on this topic but it always comes back to liability.
Thats one aspect.
Another aspect is that we have much higher expectations of machines than humans in regards to fault-tolerance.