Well it turns out there may be a good reason. According to this news item (link) a California man found he got a little more than he bargained for when he installed a new Corbin seat on his 1993 BMW motorcycle. He has now launched a lawsuit for a “persistent erection” seeking compensation for emotional distress, medical expenses and “general damages”. No mention of excessive wear and tear, although I guess that could come under general damages.
Corbin claims there is no truth to the rumour that they have now sold out of that particular seat model since the story broke.