They may not be losing much weight, but they are losing fat while gaining muscle, which is great. Muscle tissue is more dense than fat tissue, so it takes up less space. When you lose fat and gain muscle your body measurements will change, like waist circumference, even though your weight doesn't.
To see how muscle mass helps when losing weight, read more.
Muscle also requires more energy and therefore burns more calories than fat. Meaning the more muscle mass you have the faster your metabolism, which is great. If you're looking to lose weight, I think you should alter your goal to change your body composition. More muscle means you're stronger so you can work harder in your workouts too and burn more calories than before. I'd call it a win win.
If you're trying to
lose weight change your body composition and lose fat while gaining muscle, keep on exercising and counting calories to effectively lose weight. Make sure to keep your caloric intake above 1200 calories, because if you go under your body goes into famine mode and holds onto fat. Measure your progress by how your clothes feel and remember, the slower you lose weight — two pounds maximum a week — the higher your chances for keeping it off.