What exactly is a "simple diet"? Not eating certain foods? Limiting portion sizes? Research shows that traditional diets have extremelly low compliance rates.
I'm not an endocrinologist, but as far as I understand, but as far as I understand, part of the effectiveness of IF is related to Ghrelin, a hormone associated with hunger. Basically, Ghrelin is a hormone which is correlated with the feeling of hunger, and it tends to come in waves around your normal meal times. So if I normally eat at 7:00 AM, I will get a wave of Ghrelin at that time every day. But Ghrelin has the property where, if I don't eat within that period where the hormone level is peaking, eventually it will subside whether or not I have eaten. Also if I skip that meal time for a few days, eventually that peak will decrease in magnitude or will go away all together.
So this is part of the reason why IF is effective: it's actually reducing the total amount of physiological hunger I experience in a given day.