Same reason people of any nationality work in factories - because they can earn a living from it.
Many Russians work in factories.
As with the other warring countries, the women were sent to work in the war producing factories, and the men were "drafted" for military service.
factories & stuff factories & stuff
factories
There are very few factories left in London.
factories
No
German and Japanese factories
The workers of the northern factories had to work for many hours and had little rest.
Sony originated as a Japanese company, but it now has factories in several parts of the world, possibly including Germany.
Yes men and women worked in factories
pick coco beans, work in the mines, work in clothes factories, work in very cheap factories e.g. the toys that say "made in china" on them.