The human body was "designed" to maximize survival in east africa where we evolved. Early humans, and all of our primate ancestors, would have often experienced periods with limited food and thus evolved means to store energy when food is plentiful and defenses against starvation when food is not. Both of these are systems that you need to prevent from working properly to loose weight, which from the body's perspective is bad, as it is loosing its defenses against starvation.

If you simply stop eating, biological pathways will engage to reduce your metabolic rate, deprioritize some repair, and neuro-chemically prioritize your brain to search for food among many many other things. The body is preparing to last as long as possible in "starvation might be coming mode" until food can be found. None of these help you lose weight as your body is trying to play the long game - in addition to you potentially doing damage to yourself if you're missing critical nutrients.

If you run a calorie deficient, slightly under what you need to maintain weight, your body doesn't enter the "prep for imminent starvation mode" that reduces weight loss. For some people with psychological or other extenuating circumstances, starvation methods may be required under medical supervision, but essentially it is never effective for the average overweight person.