Scooter manufacturers are concerned about giving the least amount of stress to the engine. Less stress means more efficiency and more efficiency means more power. A water-cooled, fuel injected 125cc engine is beginning to gain popularity with scoots. This 125 can even out perform an air-cooled 150. So the target market really of these fuel injected/water cooled 125 are the carburated-aircooled 150s.
If a manufacturer will match fuel injection with air-cooling, they are not getting the most out of their product. The competitor will just make fuel-injected/water cooled scoots and kill the other competitors product.