The reason a person is required to import a mobile conveyance (vehicle, motorcycle, golf cart, ATV, etc.) is that if the item is coming from Canada, then it is in the Canadian commerce system. When a person imports the item into the US that item enters the US commerce system.
Once the item is in the US commerce system, the Customs Officer does not care what happens to the item. The law of 'importation' has been satisfied, thus the reason the Officer no longer has any legal interest in the item. One may sell, trade, give away, or junk out the item.
Importation of a motorcycle / vehicle for their own use is a simple process that is needlessly feared by those who have not seen how easy the process is to complete.
Lakeside