Additives or preservatives aren't likely to be the core issue. At the end of the day, by far the most significant factor for weight change is calorie intake vs expenditure. The new drugs like Semaglutide fundamentally work by significantly suppressing hunger and increasing satiety, for instance. I'm not sure what the precise data looks like, but in general, people are less social, go out less, spend a lot more time sitting on their phones or computers, and are generally a bit more stressed. All of the is going to contribute to eating more and moving less.