Symbolism, Imagery, Allegory
Carrie and Hurstwood totally love to rock out… in their rocking chairs. We might even say that we see them doing this more frequently than anything else they do in the novel. The ubiquitous rocking chair even shows up in the very last line (check out the "What's Up with the Ending" section for more on this) of the novel as the narrator tells us that Carrie is still rocking away: "In your rocking-chair, by your window, shall you dream such happiness as you may never feel" (47.125).
What could be so incredibly enticing about this piece of furniture?
One way to interpret this symbol is to think about who uses rocking chairs. Besides grannies, parents use them to try and calm or soothe their screaming babies, right? The rocking chair appears to serve a similar function in Sister Carrie. Characters retreat to the rocking chair time and time again to seek comfort and contentment in the overwhelming and sometimes dream-crushing world of the industrial city.
Interestingly, though, the rocking chair isn't exactly a symbol of pure escape from the outside world. Carrie, for example, rocks and looks out the window, contemplating what's going on outside. Hurstwood is often portrayed as rocking and reading the newspaper—a representation of the outside world. Instead of representing pure escape, the rocking chair in this way instead becomes a safe space to process the overwhelming experience of city life that so many late nineteenth-century Americans were coming to share.
In the second half of the nineteenth-century in the U.S., tons of people moved from farms or rural areas to cities in search of new opportunities (a.k.a. urbanization). On top of that, lots of immigrants moved straight to where the action was: in the cities. This was a massive, enormous, humongous (get the idea?) shift: the urban population shot from about seven million in 1865 to twenty-two million in 1890. (Source.) All of this meant that your average city slicker had to put up with lots of noise, crowds, traffic, and other potentially annoying or disorienting conditions that they may not have been used to. They probably also stepped in way more gum.
So it's safe to say that they could relate to the urge to contemplate the madness outside from the comfort of the old rocking chair.