People who override their fullness feeling do so for a reason - though many won't even register that fullness feeling anymore after years of abuse. Eating triggers your parasympathic system. Eating heavy foods and overeating even more so. It makes you sluggish, numb and forces your body into a rest-and-digest state. For someone who is under constant stress, who is constantly in flight or fight mode due to internal conflict, the fullness pain is a small price to pay for just an hour of rest from that chronic stress they feel. It's a pain they have control over, depending on how much food they stuff down their throat, compared to the non-stop state of vigilance that rules them, out of their control, normally.
In essence, it's self-medicating, in order to cope. Add to that an unawareness that this aint normal - as they usually learned this coping mechanism in childhood, a loss of meaning for the sensation of fullness to the point of not even being able to identify it anymore, as well as having no real parameters on what a normal serving for their body would even look like, and you get obesity as a result.
And it is what needs addressing. Old belief systems that are causing their stress need to be removed, self-esteem needs to be rebuilt, education on which foods will make you feel fuller and why, and re-exploration and experimentation with that feeling of fullness -as well as learning how to cope with the panic you experience once you rediscover what how urgent hunger can feel - are key to rediscovering what your body actually needs...and losing the weight.
And yes, you don't have to decide to go healthy foods, though it would help. Just like you, they can use their favourite 'bad' foods to still lose weight - they just have to learn what you already instinctively know - being overly full is unpleasant and unnecessary in life. So if you eat heavy foods, you only need so much, while lighter foods allow you to graze more as you need more of em to feel full.