As someone who eats once a day for convenience and not as a diet this misses the point of those diets. At the end of the day, the only thing that matters when losing weight is calories in and calories out. No human has ever beaten thermodynamics, and if you have then congrats on your Nobel prize
That being said, putting strict limits on your eating does two things. First, it's actually tricky to consume 2000+ calories in one sitting. Obviously people do it, and I've done it plenty of times, but most people would be miserable to regularly consume that much food in one sitting
Much more importantly in my opinion is that it forces you to pay attention to what you eat. I think a lot of people (Americans especially) consume a lot of "invisible" calories. A few chips here, a sip of soda there, a piece of candy between meetings, a red bull before shift, etc. I think many people have several hundred calories a day they consume and don't even realize that it's going into their bodies. When you make all of your consumption specific and regulated it makes those extras stand out more. I think the most successful "diets" force the person on them to mentally acknowledge everything that enters their mouth. That consciousness makes slipping in an accidental 150 calories in junk that does nothing for you harder
Cutting 1 soda per day at ~150 calories per soda is 1 lbs lost every 3 weeks. You won't feel any different without that soda after a week. In comparison burning those calories would mean around 30 minutes of walking per day. That's a lot of time regardless of how you feel. The saying goes "you can't outrun a bad diet" and intermittent fasting really succeeds at making you conscious of your consumption