Because no other piece of equipment can do what the kettlebell can. It delivers all around extreme fitness. With kettlebell training you target every aspect of fitness using functional movements. The kettlebell tightens the legs, glutes, back, arms and abs. It works your core form every angle and develops explosive hips(important for athletic competition and everyday life). It develops cardiovascular conditioning, strength, power, stability, flexibility, balance and agility. All in a 1/2 hour. So the question should be: Why NOT train with kettlebells?