[janef0421]

That would be true when purchasing a phone now, but not at the time the SE launched. At that time, the Mini had not launched, and it was not clear that any such device would launch. Since most of the people in the market for a small phone would have been using relatively old devices, most of them purchased the SE. Already having the SE would mean that few of them would want to upgrade to the Mini.

Also, it is worth noting the desire for small phones is mostly due to a desire for easier one-handed use, and the SE is as easy to use as the Mini in that regard, since the user does not need to reach the top of the device and the home button is centrally located, and thus easier to reach.