The easy explanation is that this White House is part of Tyler Perry’s movie studio and the facade is used for filming. Whether the Ds are doing anything on that set is another thing. The more people involved the harder to keep a secret.
I agree with you. However, there have been many people talking about the "fake" White House. I submit that if it happened, it only was used once on Inauguration Day, because they knew with all the activities on that day, that Biden wouldn't be able to do the "Day One" signing without major slip-ups, and so they took advantage of the Tyler Perry location being in Atlanta, and Joe being there for the Senators, to film the "Day One" signings of EOs.
There was a video showing the main part of the White House and then the camera panned too fast across the Rose Garden to the outside door of the Oval Office as the door opened and a crowd of reporters plus the guy with the camera went into the Office with Joe sitting there with the stack of EOs for him to sign. The weather outside was nice, and I tried to slow down the panning to see what they might be hiding. I could make out what appeared to be a blurred look at a parking lot with several cars parked right outside the Oval Office. There was also no Marine Guard on the Oval Office door.
So what I am saying is that I have not heard of Joe being in the vicinity of Culver City during the campaign or after, so if a fake White House was used, it would have been the Tyler Perry one.