I think the lack of purpose thing is important in factory workers. This is why they lack incentive.

The pay... I'm not sure that really matters. I mean wealth is relative. Someone earning £1000 a week, being offered a £5k performance bonus, might be more motivated to earn that reward than someone who is earning £10k a week and offered a £20k bonus. It's five weeks wages to the former, and two to the latter. People's idea of "a lot of money" differs drastically depending largely on income.