I have been around motorcycles/motorcycling for a long time. I fell in love with the concept of man and machine back when motorcycles were just motorcycles. They were not sport touring bikes, or sport bikes, touring bikes or any other category. In fact when I fell in love with motorcycles Harleys were not even called cruisers, they were just motorcycles.
Back then you bought a bike, say a 1977 Suzuki GS 400 (My first non enduro street bike) and you made it do what you wanted it to do. That meant I added a rack and sissy bar to it for when I wanted to carry things, and a bolt on windshield for touring. You had to have a certain amount of imagination, mechanical skill and, most importantly, no preconceived notion of how good it was supposed to work when you were done. You just believed that the mods you made were the right changes to transform your bike.
Then the Gold Wing came along. And the Yamaha Virago. And the Suzuki GSXR. And then the Kawasaki Ninja. Suddenly there were sub categories and specialized motorcycles. The UJM(universal Japanese motorcycle--a basic, standard style bike), the bread and butter of the motorcycle industry quickly disappeared and good or bad, categories were created.
Side note here for you non-riding or just bought a Harley because they are cool folks: Ninja is not a style of motorcycle, its a sub brand at Kawasaki. That said, Ninja does not automatically mean full-sport race bike. Examples include the Ninja 1000 ( a sport touring bike) and the ZX14R, a much more drag bike than sport racing bike, as well as the Ninja 650,a wonderful commuter bike and the Ninja 300, a great beginners/commuter bike. And a Suzuki GSXR is not a Ninja. Nor is a Honda CBR a Ninja. Because it has a fairing and sporty lines does not make it a race bike. Take a quick look at the handlebars. If they are above the triple tree by an inch to three inches, sport/commuter. Clip on bars, under the triple tree? Race bike.
From the specialized categories, sub sub categories were developed. Sport Touring bike came along as the riding population realized they needed bikes to go as far as they used to as UJMs. The aftermarket responded with handlebar risers, footpeg lowering kits and wonderful detachable soft luggage. All this aftermarket excitement led manufactures to build purposeful sport touring bikes. And harder edge sport bikes. And cruisers that are more cruiser(y). The only thing that was left alone for the longest time was the enduro world. These bikes were still just dirt bikes with lights. Light, agile and fun to bash around on. Then somebody went and traveled on a dual purpose/enduro bike.
Suddenly a new category of large adventure bikes was born. In all fairness BMW invented this category in the mid-90s, but only engineers rode BMWs back then so no one really knew. Now, I have to say I am split on this category because the size of these bikes--Suzuki Vstrom, Triumph 800 Adventure, Yamaha Genre and many more, well off roading with them would be an adventure for sure. But on the other side, they are big, comfortable and functional bikes. You can whip one through a canyon dragging footpegs one day and then bomb out a 700 mile day the next. Its almost as if the UJM has come back around--with semi knobbies and hand protectors. Even Ducati, Aprilla and Moto Guzzi have adventure-esque bikes in their line up. This is a fast growing segment of the market because people seem to like riding comfortably and still having fun--imagine that, fun on motorcycles.
So, diatribe concluded, what did we learn? There are many types of motorcycles and as they say in the Motorcycle Safety Foundation, The More You Know, the Better It Gets.