Because they know that strength training will lead to smaller, stronger you (not the Incredible Hulk you).
They know you will lose weight faster because more muscle means a higher metabolism, therefore maximising your body's fat-burning potential!
And they know that strength training will help you build a strong, toned look - this is not going to happen through cardio alone!
But it's not just about how you look - strength training gives you an incredible sense of achievement, power, excitement and will really impact on your day to day life in a positive way!
So head for the dumbbells, kettle bells or use your own body weight. You can't go wrong.