It makes it a slider food - high calorie, but easier to get in without those inconvenient lumps or chewing that slow people down and give time for the full signal to reach the brain.
Like how even if somebody can feel stuffed, they may find that there's always room for some ice cream.
There are a lot of people who sabotage their weightloss by doing their best to find a means of getting maximum fat/sugar/calories in as possible because the emotional and psychological pull of those tastes and sensations outweighs even the surgery that's been designed to prevent them getting pleasure from eating as they had done up to that point. And others are sabotaging it because their original overeating was a deliberate act of self harm for such reasons as a reaction to historical or current abuse, violence or other psychological damage. Some even have to deal with partners still trying to keep them consuming excessive calories by presenting them with blended 'freakshakes' saying 'look, aren't I kind? I've found a way for you to still have things that make you happy' (and therefore damaging the person's self esteem and leading them to potentially give up).
Without intensive support for the emotional issues and trauma that may have led to them being there in the first place and to deal with the consequences of a) not being able to self soothe with food and b) loose skin, scarring, pain, nausea, malnutrition, etc, success is certainly not guaranteed by any stretch.
I don't think it's an easy option at all, even if that is how it can be presented 'Do this and you'll be slim by magic and never need to worry about being fat again' - it's brutal surgery that carries significant risks both in the operating theatre and afterwards and requires the person to always be aware of harm, pain and unpleasant sensations when they eat.