Examining registration data for classic motorcycles (built before 1981) shows us that, on average, about 43 percent of motorcycles survive past 12 years of age. This is about 2/3 the life of a car.
This graph starts with classic bikes that were registered in 1992, then shows how quickly each make falls off on average. Surprisingly, the bikes with the most staying power haven’t been Japanese or German but good-old American Harley-Davidsons, and by a wide margin. If a Harley-Davidson made it past 12 years old, it had a 75 percent chance of making it all the way to 25 years.
Japanese motorcycles benefit from generally high standards of build quality, but are also often cheaper, ridden hard and sometimes crashed. Harleys, on the other hand, tend to enjoy more careful ownership. Their owners are also inclined to just enjoy the act of riding rather than trying to qualify for Moto GP every time they saddle up. Ultimately, it seems that the disparity is due to Harley primarily building cruisers while many imports market far more sport bikes appealing to folks who like more speed and risk.
Hondas enjoyed the highest survival rates of Japanese motorcycles, due possibly in part to their big touring bikes like the Gold Wing, which like Harleys more often have careful long-term owners. As for Yamaha, only 30 percent of their bikes that made it to 12 years old then made it to 25.