Like the saying what comes around goes around, a lot of the bikes go in and out of fashion, big trailies were never in fashion in the UK but were in Europe, now they are coming into fashion in the UK, the naked bike goes in and out of fashion regular, the sports bike won't disappear but as the markets change due to emissions etc the sports bikes will change to suit. As most bikes now are sold as a leisure item the bike will evolve in that way, hence why there are more bikes that are naked. And as most bikes have lost their sole manufacturers have realised this after smaller companies like triumph have made a bike with sole in the engine department they have had to follow suit, also the 3 cylinder engine has some of the good points of 4 cylinders and 2 cylinders but with some character and also tend to use less fuel due to less frictional loss over a 4 cylinder engine, even car manufactures are going the 3 cylinder route