Umm, I'm thinking, but the best I can come up with:
1. Rural/extremely out-of-the-way locations. Which means that locating a Redbox that is profitable is going to be extremely difficult because by definition you're in low-density areas.
2. Extremely poor people. Even most lower class people have cell phones these days where you can watch video, so the number of people in reasonably dense areas who can't afford broadband is going to be very low.
I do think the "multiple subscription services" issue is a valid point, but in general I think that most Redbox users are likely just slow adopters, similar to folks with landlines. The problem is that customer base slowly but surely goes away.