Last year there were a lot of random original rooms that were "cameras down" and we asked about it.
In addition to what you said, our guide said they were worried about the "technology" in the rooms. Seemed like an odd term so we asked for clarification and he said something along the lines of (paraphrasing as I really don't think I accurately remember it):
"Stuff like mirrors for a depth gag, where our cameras and triggers are, or how we have a scareactor positioned to make multiple scares, skrim (or whatever the false walls are that lit up you can see through) or false boo holes you can see."
Gave lots of examples, but we had asked late in the 6-house tour after lots of "cameras down" rooms. So I think another reason, and why some originals have a lot of rooms "cameras down" is that they are trying out new ideas that they don't want other haunts to steal (of course, sending one spy through the house would reveal them so that kinda kills the argument - why take away the value of thousands of people paying for the tour for something that could easily be found out by having a spy going through the house or doing the UTH tour). There were a lot of rooms, at least in my experience last year, that you were allowed to take pictures in a certain direction...or cropping out a certain thing...so I kinda believe what they said.