There are a couple of reasons. The main reason is that I live in Florida, and I prefer to keep native species. Often people come over to our house, and they have a lot of questions about our pets (marine aquariums, turtles). I try to make it somewhat educational about local species. The second reason is that they rarely exceed 2 feet.
The snake will be fed a mixed diet, but I wanted it to accept lizards, to show their more natural diet.
I have lots of experience keeping herps. I had as many as 35 snakes at one point (too many). I got out of the hobby about 7 years ago, when I got married. I just convinced my wife to let me keep one "pretty little snake".