Doug-
I think the vast majority don't die, they go into hibernation of sorts.
The owner stops riding on a regular basis, bike goes from the house to the garage.
Its status is reviewed from time to time, and kept as it was/is useful just no time at the present to use it.
Have three neighbors who have top line or custom bikes that are kept for their potential future use.
As to the stolen ones, just hope/expect mine show up on ebay one day.
John Jorgensen
Palos Verdes Ca USA