Except that the human body is way more complicated than that. Whenever you try to increase calories out by exercise, your body just finds somewhere else it can economize, because it wants to operate on a fixed budget. This can include pulling calories from your immune system, or making you subconsciously move less throughout the day, or even sleep more. You can only overcome this for a limited time. Kurzgesagt has a good video on this phenomenon. What you actually want to do is reduce calorie intake.

Exercise is good for lots of reasons, but it isn't a good way of losing weight long term.