There are good factory workers, and bad factory workers. On one side you have those that do the absolute minimum (just like any job), while on the other you have people that know how to work more machines and are more helpful in diagnosing production issues etc.

The flaw here is that the only thing that matters is how long you've been hired. Not how good you are. Similar to teachers. Higher pay, shift preference, vacation scheduling, overtime availability, it all goes to the senior employees.