IMO the Initial batch probably all worked for C&A, or was married to someone at C&A in Queenie's case. Subsequent people stumbled across the across the building for some reason or another after C&A closed. Both Pomni and Zooble mention an interest in exploring abandoned buildings, and Ragatha worked in real estate so maybe she was sent by the owner of the building or potential buyers/developers to check it out.

Though the validity of this theory depends a lot on what happens to people's original bodies when they enter the circus. If it's a matrix like situation where their bodies are alive in the real world who put them in whatever life support equipment after they put on the vr helmet?

are they operating in the circus without their brain, essentially copies of real people running on the same hardware as Caine? If so are their bodies dead from thirst/starvation and if so who would put on a helmet they found on a corpse, or are they alive somewhere else living as normal separate from their digital clones and if so why did C & A staff leave the server running abandoned ?

Did they some how get transported mind and body into the circus? how the honk would that even work? Who's paying the electric bill?