In The Jungle, Upton Sinclair is not merely reporting on terrible working conditions in Chicago's slums. He is not just informing his readers about poor sanitation and hygiene in the meatpacking process. He is trying to transform the entire economic system of the United States. To achieve this huge task, he jams in example after example of economic exploitation – for example, Jack Duane's stolen telegraph patents, Ona's sexual harassment from her boss, and the French immigrant in Marija's brothel who is kept locked up and forced into prostitution.
At the level of the sentence, this attention to detail demands verboseness (a.k.a. a lot of words). Take, for example, this passage about Jurgis joining his first union:
He never missed a meeting, however. He had picked up a few words of English by this time, and friends would help him to understand. They were often very turbulent meetings, with half a dozen men declaiming at once, in as many dialects of English, but the speakers were all desperately in earnest, and Jurgis was in earnest, too, for he understood that a fight was on, and that it was his fight. (8.17)
This passage is unusual in that it is not describing the horrors of life in Packingtown, unlike most other passages in The Jungle. Still, it does illustrate what we mean about Sinclair's incredible wordiness. Check out that third sentence: it has six separate clauses! It's almost a run-on sentence; it just keeps going. It's as though Sinclair cannot contain his excitement in a single declarative sentence; he has to add comma after comma to tack on new observations and ideas to make his point.