Typically the type of rider who rides without a helmet has some sort of other protection from the wind in the form of a windscreen or fairings on the motorcycle to deflect wind away from their face. It’s mostly a comfort thing though because it’s not impossible to ride without a helmet even without wind protection especially if you’re just cruising around town at lower speeds.

Even people who do wear helmets appreciate these features on their motorcycles because having the wind blasting against your helmet can be very loud and tire out your neck muscles.