Wrong. It has everything to do with how you're eating, when you're eating and what you're eating. No fuckin' shit a person isn't going to lose weight on 1500 calories because their body is in catabolic state, trying to hold onto and create as much fat for self-preservation. Especially if all 1500 of those calories are carbs and fat. Nevermind if they lack any exercise thus fail to expend any of those 1500 calories.

Cardio is to account for excess calories you've either taken in or failed to burn off through regular weight lifting. As has been stated, to force yourself into a caloric deficit if your diet stays the same. It also has numerous potential benefits to your cardiovascular system and endurance levels, but that's irrelevant from the primary point.