If I understand right, all these cities rated as amomg the most depressed so even though some cities received an A in these ratings that means they're depressing cities but just not as bad as the others?
Because you'll find clinical depression in varying degrees pretty much anyplace you go, my guess is that what the authors of this survey did in order to make the study manageable was to first take the top 101 US cities by population and then extract the statistical data from those cities. Just because a city or town isn't listed here doesn't mean that there's no instance of clinical depression there, only that it wasn't included in the survey due to population limitations or whatever initial sorting criteria they used.