One commonality between the spaces that exist in the back rooms are ones that emulate doctors offices, malls, corridors, pools, playgrounds, etc. all of these are either public or pseudo public spaces (like big box stores). Also there is a nostalgic quality to them, they all exist in a “built in the past” sort of context.
I think a major aspect is the idea of being trapped in a liminal space, one which has the perceptual quality of being a transitory space. You cannot return to the place from you came, but you also cannot move on to your destination.
In a sense, the Backrooms could be seen as a metaphor for the sense of feeling trapped in the awkward, transitional period of being a teenager. Unable to return to the comfort and security of childhood, but also not yet able to move on to adulthood. That many teens also feel as though their future has been stolen from them probably also connects to the corporate-coded aesthetics of the Backrooms.