From an evolutionary standpoint, less eating restraint may be linked to increased survival rares in times of scarcity, as stored energy in fat provides a clear advantage. Nowadays, in first world countries, food is everywhere and "overeating" becomes much easier.
Additives for food security is an intetrsting angle, thanks. That being said, I'm not convinced that it requires making fattening products, but it was in part the outcome.
Your last point is at least partially mitigated by the fact that food intake regulation factors in physical activity in most people.
- Extremely high levels of food security in developed nations. It's hard to get fat when food isn't available.
- Related, nutritionally-questionable food products that were used to achieve this food security (primarily mass-preserved and processed foods).
- A transition from jobs requiring large amounts of physical labor to those that require little or none.
That's just what I can think of off the top of my head. Like most societal problems, the causes are myriad and complex.