Because of the environment of gas stations (easy to get in and out, open all the time, has cash on hand, not at the top of society) they typically already have

Because of the environment of gas stations (easy to get in and out, open all the time, has cash on hand, not at the top of society) they typically already have really good cash handling procedures in place. They are already paying for cash to get in and out quickly and securely so I think when compared to something with similar margins and volumes like a grocery store, it makes more sense to push for more cash via discount vs a grocery store. As an anecdote, I don't think I've seen a grocery store offer a cash discount whereas I've seen it offered at gas stations frequently.