Yogurt is interesting because it’s already acidic, and dairy contains proteins, salts, and acids that buffer pH. So the microbes that thrive in that environment are already able to handle more acidic environments generally, and then might not experience as acidic of an environment in the human stomach compared to some other foods.

A lot of probiotic foods don’t actually have more microbes in them, but have certain microbes that tend to be found in human guts. I wonder if there’s some kind of filter effect where only certain types of microbes are more likely to survive the stomach, and therefore our guts tend to consist of microbes that are hardy against those conditions.