There are actually a lot of great details here it's not slop like I was expecting. Won't write out all the cute jokes (like the fake throne turning into real metal etc) and stuff ("why seagulls" etc) but note that Async guy lives near enough to Clark's business to see his ad. That means it's a localized issue.

Predictions in order of decreasing seriousness: they can't control the spread or turn it off but want to handle the issue privately (they aren't sending in swat teams), they are deliberately keeping the backrooms turned on because they either want to salvage investment or make use of the duplication, Clark was "chosen" because he has architect training and a therapist going in will have a similarly weird effect, Mary's mother went inside leading to her agoraphobia (a bit trite as that's kind of the opposite of an inside-only dimension), Mary will reappear as a member of the research team studying the mental properties of the dimension, there will be new viruses/bacteria/prions/parasites misduplicated that cause the most horrific diseases imaginable, there will be rare materials found within the structures, there will be Backrooms-tainium, someone from Async will say The Backrooms Project (please no)

If you're curious about why this movie in particular compels me to be normal on here for once, I don't care. Did you think it was slop? Whaddya notice? Elucidate my plotcel nonexistent ass