The factory is not dealing with a fixed pool, the factory creates things.
If the bosses treat their workers better, then their workers CAN, and perhaps will, create MORE things. Because as a worker I have some power. I can strive to increase production and work hard, or I can slack, or otherwise deliberately strive to reduce production.
Further, I cut them in ways where they didn't even know they were bleeding.
And that wasn't the first time. At my first factory job in a satellite dish factory. When we had a holiday, the factory bosses would make us work nine hour shifts on the other four days, because they could get four hours of extra production without paying overtime for it.
Personally, I thought the longer work days sucked and it pissed me off that they ruined my four day week that way. So I did my best to only get 8 hours worth of production done in the nine hours.
In some ways though, I am not sure they cared. After they laid a bunch of us off (they were making BIG satellite dishes, after all, and that market kinda collapsed). I stopped by one day and asked to see their numbers. They had two people producing 1400 on the drill presses. I could do 1200 by myself no sweat. It would make sense, if they cared about production to get rid of one of those two and hire me, but they didn't want to do that.