As noted, it's an appearance thing. The riding position on a contemporary "chopper" (think reality TV shows) is low bars, arms forward, legs forward. It bends the entire body into a big "C" shape. Not comfortable for any distance, at least for us old and inflexible guys.

Look at the size of the fuel tank on the photos SwampYank posted - see how small it is on the modern, low bar chopper? These bikes frequently have an operating range of less than 100 miles. They ain't made for going very far. Distance riders favor mounts like the goldwing, big Harley baggers, or BMW sport-tourers - all of which have very different ergonomics than these bikes.