JWs did not "outgrow" the property. All circuits that attended on rotation nearly every weekend only filled the place to 70% capacity. Once upon a time in its heyday it was full because circuits were not divided into A and B parts as they were when the property sold. It had a full cafeteria that served elaborate hot meals, breakfast, lunch and dinner on lengthy assembly days in the 70s. Also consession stands (4 or 5?)around the perimeter of the hall served all the regular food stuffs Watchtower was known for before that was all done away with. Overnight camping was also the norm in the upper parking lot in the 70s to early 80s. It was actually fun times for us kids.
Not many people know how the building was constructed. A massive mound of dirt was made and then reinforced concrete poured to create the dome. The dirt was removed and the hall finished. The atrium arch was done the same. As kids we would scale the dome and get in massive trouble.
The property manager(I won't disclose his name) lived in the apartments by the upper parking lot. He was made an offer for the property and forwarded to the Watchtower. They took the offer. The building was plowed and high end condos stand in its place.