I think there has been a sea-change in people's attitudes to food over the last 50 years.
When I was a child, my parents didn't have much money, like most other people. Being greedy, taking the last slice of bread when you'd already had two, or helping yourself to something over and above your 'ration' was deplored and would bring on a telling-off, being told not to be greedy.
The point was that if you ate more than your fair share, you were essentially depriving another family member of their share.
Although there are still families who struggle to put food on the table, generally speaking food is much more available and affordable than it used to be.
There's also been a change in attitude towards ourselves, with much more emphasis on it being ok to treat ourselves to things which our mothers (well mine anyway) would have considered both a waste of money and an expression of personal vanity - the 'because you're worth it' philosophy.
Women of my mother's generation didn't think they were 'worth it' - they thought it extravagant to spend money on cosmetics, skin care, hair products etc.
Translate this change of attitude into food consumption, and it becomes another factor in why some people overeat. Nowadays, it's easy to persuade yourself that it's not being greedy to eat that extra piece of cake, it's simply that you're worth it/you've had a hard day/ you deserve it.