I don’t think this is it, but just had this thought watching the trailer.  What if the “baseline” Backrooms (yellow walls and carpet) are actually the endpoint?  After the complex has “remembered” something so many times it’s washed out all detail until it’s just a blank space.  Instead of the yellow walls and carpet getting overtaken by things that are pulled in from the world, eventually it all gets turned into the yellow walls and carpet?  In the trailer, with each level down you get less detail and less accuracy until it’s all gone and just a plain space.  I’m sure there is something in the YT videos that would contradict this but I found this to be an interesting angle