For a lot of people these bikes were just expensive toys. Motorcycling is not in their blood. Don't know if that's the case with your PO, just saying...
They were relatively inexpensive for their high profile wow factor. Anyone could buy a CB750, and it was recognizable as something special. Then once the new wears off, they got pushed into the corner. And the PO bot a jet ski or some such.
At the time they were parked they weren't even worth enough for the PO to try and sell it. And often there was just the little lingering feeling that, "someday I may want to ride it again". And some good memories.
And one by one they will be repurchased, and restored, by those who do have it in their blood.