I wonder if originally it's placement was an attempt to keep an eye on the spare lest it get stolen, a easier thing to have happen unnoticed if stored in the rear of a vehicle. It would be an interesting test to have a number of drivers take a vehicle for a short drive then while they are away from the vehicle remove the spare and see how many notice its gone?? and at what point , approching the vehicle , seated inside or not until they are driving ?