Food deserts do exist but appear to have no meaningful effect on eating habits.
https://news.uchicago.edu/story/food-deserts-not-blame-growi...
https://news.uchicago.edu/story/food-deserts-not-blame-growi...
I am not sure why you mention eating habits, since this is not what is being discussed
Actually, you pointed out that food deserts exist, and asserted that that meant that plain yogurt is not generally available, the thing you pointed out does not support the conclusion drawn from it.
But you don't have to take my word for it. Instead of making things up you can literally just go look.