Why do you think the workers in these factories accepted these conditions and did not quit? in the story "The Jungle"

They probably had no other choice. During that time, it was hard to get a job with a solid pay for many people (especially immigrants). If they decided to quit, they would have to find other jobs, which probably have bad conditions as well. If they couldn't find any good jobs, then they would basically become homeless and wouldn't be able to pay for themselves and their families. (Back then, families were much more important.)