Poor kids in Africa, don't want roller-blades. Nobody born before 1985 ever asked their parents for roller-blades for Christmas. Bikes come in more colors. Can't roller-blade in snow. Can't ride roller-blades on the beach.
Bikes have front and rear brakes.
Never seen a car with roller-blades strapped to it's roof. Nobody ever rode a bike to disco music. A triathlon does not include blading. You can still ride a bike that isn't your size. Can't use your arms to help you blade uphill.