Exercise on its own doesn't lead to weight loss (in order to burn the necessary calories, you'd have to be exercising all day long), but it is not uncommon for exercise to suppress appetite, thereby reducing the calories in component of the weight loss equation. Unless of course hunger signals are being ignored, as in the case of unconscious, binge, or comfort eating.
> Exercise on its own doesn't lead to weight loss (in order to burn the necessary calories, you'd have to be exercising all day long)
Assuming that you were in perfect calorie balance before, any additional exercise without additional calorie consumption will produce a calorie deficit. This may or may not produce weight loss depending on the exercise profile and a lot of other factors (including, IIRC, what and when you eat relative to when and how you exercise), since its possible to gain weight with a calorie deficit while if you are building muscle fat enough (since fat stores more energy per unit mass than muscle.)
To be sure, there are many factors. But going by what a lot of people do, they will get a workout of thirty minutes burning maybe 200-300 calories, then reward themselves with a Big Mac at 550 calories, and they probably already had a caloric intake in excess of maintenance (hence why they are exercising to lose weight, and more likely to go for that reward). Heck, even one Snickers[1] bar can counteract that workout. Not saying this is everyone, but it seems to be a common pattern: most people don't realize they need to control their intake, even if they don't reduce it, otherwise all the exercise in the world won't lead to weight loss.
> But going by what a lot of people do, they will get a workout of thirty minutes burning maybe 200-300 calories, then reward themselves with a Big Mac at 550 calories,
The effect of exercise plus an additional Big Mac does not reinforce the claim that "exercise on its own doesn't lead to weight loss", because "plus a Big Mac" is not "on its own".
> and they probably already had a caloric intake in excess of maintenance (hence why they are exercising to lose weight, and more likely to go for that reward)
The reason why they are exercising to lose weight is probably that they have a current weight above their desired weight. That doesn't mean that they have a current calorie surplus -- plenty of people seek to lose weight when their current weight is stable but above their desired weight.
