There are a few main reasons for the bike you drive:
* Environment
* Mileage
* Looks
* Usefulness
Today, sport bikes are dominating the market as they are often very fuel efficient, got nice looks and are often very high quality and power.
People ride cruisers because of the laid-back feeling and comfort you get.
People ride enduro/cross bikes if they live in rural areas, as the bike is more versatile and easier to ride offroad or at bad road conditions.
People who live in cities often choose to drive scooters because of their fuel usage and easiness to use. In the city you need to de-accelerate a lot and would therefore also need to shift gears a lot. Therefore a scooter is more comfortable and easy to ride.