It costs a lot of money to make multiple versions of something, compared to having just one version. The amount of profit they were getting from the mini wasn't enough compared to the regular model, and they correctly deduced that if they eliminated the mini, everyone would just buy the larger model instead so they could decrease their manufacturing and design costs.

If you're an Apple user, would you switch to Android just to get a smaller phone? Or would you just bite the bullet and get the larger iPhone after the mini is discontinued? Apple knows that 99.99% of Apple users are in the second group.