As a rule of the thumb, the longer your stomach (and its bacteria) have to work to get calories extracted from a food (this has a big correlation with the food not being excessively pre-processed, and also has a big correlation with lack of additives) - the better it is for you. :)
We will surely learn the precise reasons later. Until then, acting upon that information is possible without knowing why. :)
I think the reason for it is the fact a diverse gut micro biome is healthy for you. They have so many posistive benefits from helping fight infections to taking up space so bad bacteria don't show up.
They have studied the gut micro biome in many people and even noticed certain bacteria are higher for individuals that "usually eat whatever they want" type of people.