There is not specific activity that makes you lose weight. It's important to understand that the "slim legs workouts", "fat loss workout", "weight loss workout", are just click bite to bring your attention to those workouts. There is not ONE specific activity to achieve such thing.
In order to lose weight you must be in a calorie deficit. Yes, exercise affects your energy expenditure but is exercise what really makes the big difference in your overall calorie expenditure?
The answer is no.
Your basal metabolic rate is what has a bigger impact on your calorie expenditure. How active you are aside from your workouts also is.
With time, as you build more muscle mass and manage to have a healthy or lower fat % the more efficiently your body will use energy in a resting state (muscle requires more energy at rest than fat). Resulting this in a higher metabolic rate.
Something important to mention is that you can't manipulate your metabolic rate. You have little or non control over it. However, there are certain things that you can avoid to stop slowing down your metabolism over time. Based on research, some of those things are drastic weight loss programs or crash diets.
Exercise is awesome and I think the best advice I can give to people is to exercise but generally thinking that a specific exercise or workout is the magic pill for your weight loss or even worst, the magic pill to lose fat on your thighs or arms, it's just not right.
A person that doesn't exercise but manages to be in a calorie deficit can lose weight.
What will happen with the type of exercises or workouts you choose to do is that they will affect your body composition, fat muscle ratio (shape) an aid calorie output.
Different activities have different benefits and impact your body in different ways.