If the media helicopters were flying low enough to see what one reporter believed to be girls clothing in the creek, I think they'd have spotted any other areas the were taped off as a crime scene, along with the large presence of crime scene investigators and other personnel. The actual location of death is very important in terms of forensic and medical examination, probably more so than a secondary location, if the bodies are moved. It connects the perpetrator directly to the murder, as opposed the far lesser crime of being involved by moving a dead body. The two weeks they spent "turning over every leaf" at the crime scene suggests they were incredibly thorough at that location because it was also the site of a homicide. If there was a primary location in an outside building, it wouldn't really make sense that they'd spend hardly any time processing that as opposed to the lesser crime scene because that's be where the most important evidence to prosecute the perpetrator would be found.
I also think this case would be moving forward at a distinct disadvantage if the known location of the homicide was elsewhere and kept secret, considering the energy that LE has put into pleading for tips.
The origins of outbuilding theory iirc began with Abby's death occuring a day later, which was also debunked by the legal information in the Petition to Seal the Autopsy Report.