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 it’s more that these are big empty places that are usually full of people. So they’re familiar but not, it’s like uncanny valley for buildings.
Also I feel like it’s somewhat related to megalophobia and submechanophobia? At least the pool ones strike me as that.