Expensive. Thus not everyone can afford one or have experience owning one.
Even if you pony up and make the purchase they have expensive maintenance requirements which can really add up and I think that limits how many miles the actual owners do put on them.
I have a friend who has owned 3 Ducatis (2- 900ss and 1- 750SS) and he really likes them. He raced one and currently has one for the street. He also rode it from where he bought it in North Carolina home to SW Arkansas!
Like a fine wine they are kind of an aquired taste.