I'd say mostly age group and "health" (with a good chunk of price point). Specifically, for the under-7 crowd. It doesn't have hinges, so fewer parts for small children to break. It doesn't have 3D, so the possible vision damage stops being an issue[1]. It's cheaper, so parents are more likely to purchase it. Oh, and it's coming out on the same date as Pokemon X and Y.

[1] http://games.yahoo.com/blogs/plugged-in/nintendo-3ds-young-e...