Not an expert but I think ultra processed food has two main aspects, one is additives and preservatives. And the other is our body doesn’t need to process it as much to digest it. If you eta rice/bread your body has to break that carbohydrates into glucose which takes energy. Now if you directly take suger/glucose then eating the same calories would be a lot more plus calories since your body doesn’t need to work hard to process it. Furthermore it has more pure calories per same weight, so you end up consuming more to feel full compared to eating something not as calories dense.
Or let people with money/power now write whatever they want. Because who is going to stop them?