I can simplify a lot of it. Sugar and salt. Both of those ingredients are the primary drivers of the effect you're talking about. The other ingredients people tend to fixate on are often red herrings in this discussion. If you dig in depth, they have long track records of use and few if any reports of any harm being attributed to them. Lots of conspiracies, not a lot of hard scientific data. But with sugar and salt, the data on triggering the reward centers of the brain is crystal clear - and we all know it. We can taste the difference, which is why companies market test their food to include it, and why we, as consumers eagerly buy it.