Well that's my point, rather than worry about 'what happens if I get hungry and I don't have a jab to suppress it?', I make sure what i'm eating doesn't consistently leave me feeling hungry.
I don't just eat empty calories until I hit 1500 and then sit feeling like i'm starving for the rest of the day (which is what would happen if I didn't change the things I ate), I deal with 'feeling hungry' by eating food that helps stop that happening in the first place, even though i'm in a calorie deficit.
It's infinitely easier to have the 'willpower' to plan out some good food for the week/day when you're not already hungry, than try to deal with the effect of being hungry later, then you don't find yourself needing that willpower to not eat when you're hungry.
Even the people with the best willpower in the world are going to have a miserable time if they let themselves constantly feel hungry because they've eaten empty calories and nothing they're eating makes them feel full. This is probably a big part of why some people find it easier than others to rely on 'willpower' - if your diet is mostly whole foods and you feel full and satisfied after even smallish portions, then you don't need much in the way of willpower anyway, because there's less of a feeling to fight against.