Originally Posted by ph0rk
The United States is hardly the only country where motorcycles are sold.
Further, motorcycles last a lot longer than they used to, so there are many more good-quality used bikes to be had. Obviously, this will eat into new bike sales.
I'm not seeing a problem, other than the OP referring to motorcycling as a "sport".
Quoted for truth.
There are already a number of bikes that are viable to be sold in Europe but don't make it to the American market. This reflects differing cultural tastes. These tastes could vary across time as well as they vary across geography, with the end result being the same: Everyone gets what they want.
Car sales will also decline as cars become more durable - this doesn't make the car industry "doomed". As cars last longer and are made with higher quality standards, their increase in price slightly outpaces inflation. Same thing with motorcycles. Put simply, manufacturers will get just as much money out of you, even if they sell you fewer vehicles (most of which will last longer than before).
More bright side: The ADV class of motorcycles has really blossomed over the last ten or twenty years. For as long as there is a demand for motorcycles, there will be a market. New models are introduced all the time and the only reason why a manufacturer would retire a model is if there is little demand.