I don't buy that they "forgot they were full" because of diminished short term memory. When people overeat, I do not buy that it is because they actually forgot that they already ate.
Some other brain effect could make sense, but this one seems weak.
IIRC around 20-30% obese people have ADHD, and they use food as a form of self-medication when their dopamine levels get low.
Unfortunately it's not screened for in obese people, so most of them never get tested :(
Myself, once I began meds, the need to eat constantly evaporated. The first month I felt no hunger whatsoever (I guess there was no dopamine deficiency any more, and regular hunger systems still haven't kicked in), and after that time my hunger got to normal levels - meaning, the weight stabilised, and now I eat only when truly hungry.
Some other brain effect could make sense, but this one seems weak.