That's people customing their motorcycle, not HD manufacturing a motorcycle.

 

Still the same answer, different look, different style...shiny paint, denim paint....spoked wheels, mag wheels....chrome, blacked out....big wheels, small wheels. They try to figure out what look sells and give the customers options otherwise everything would always look the same Vehicles used to have 14" and 15" wheels, now 17", 18", 19", even 20" is common now. The larger rim with low profile tires is what's popular now, it's the look people want.