I remember living in a rural area where people couldn't afford a car, but could walk to a gas station and pay 3x the prices on everything compared to if they bought everything at grocery store - it just helps keep them poor. And often, I think people see "dollar" in the name, and think that automatically means cheap, but being poor doesn't mean being financially literate.
If people weren't segregated into rich areas | poor areas, or maybe grocery stores found some other way to be profitable in low income areas, or some other thing, this wouldn't be such a problem. But as it is right now, they are filling a need, granted with negative side effects.
Edit: I realize the article focuses more on Dollar Generals causing food desserts, rather than being a response to them. Guess I'm focusing on more what I've seen.