How?

1. Bliss point - the amount of an ingredient (salt/sugar/fat) which optimises deliciousness
2. Texture - soft foods require less chewing, so we eat more food
3. Marketing - Colourful packaging, cartoons to market to kids, etc.

Ultraprocessed food uses all of these things to be just irresistible. The industry uses many of the items from the cigarette industry playbook - denying addiction, different packaging and so on.

I saw this documentary (Irresistible: Why We Can’t Stop Eating) which talked about these points in detail.