Before I retired, I worked in a factory, on the production lines. When I started there in 2002, we had about 100 people on each shift on the lines plus support people. When I retired, two years ago, we were down to 6. Those 6 spent their time looking at computer screens.
There are two big drawbacks. 1) the machines need to work all day every day to cover the very high capital costs. You cannot lay them off if the work dries up. Our work was seasonal but they need to keep those machines working regardless. 2) as Overread mentioned, machines are not adaptable. We could switch from product A to product B in a matter of minutes when I was running a team of 40 people. The machines need to be reset and readjusted which can take hours.