The processed and chemicals may be a proxy for high calories low nutrition, but generally they are used to create hyper palatable foods that are low nutrition. In general, it's quite hard and expensive to produce high palatable foods using real ingredients; food engineering changes that and makes it easy for cheap food to mess with our senses. As far as I can tell, this is the generally accepted argument for the problems with UPFs - they make people want to eat more cheap crap food.