You mean why not use the Arduino IDE?
Too steep a learning curve for beginners. I see people come here all the time and ask "How can I do two things at once in my program?" because they want to blink an LED and read an input but the LED example uses a delay statement.
My scripting language will do away with the delay statement. It will have timers. You reset a timer, and then it starts counting up. When the time equals how long you wanted to wait, you then perform your task and reset it again.
Presenting a user with my whole code base for reading the SD card and updating the sounds, and the servos, and checking for input, and updating the LEDs would also be incredibly confusing, even if I tell them that the only thing they need ever do is touch the code in one function. Hell, I'd be confused if someone handed me their huge program and told me to just start adding code in some function.
Doing things this way hides all that from them. They won't fret over it because they won't see it. They won't need to worry about installing the compiler. Configuring it. Installing any necessary drivers. Getting it to upload to their board properly. And I won't need to include a USB port and all the support circuitry for that, which I don't have the room for, and which would add additional expense and complexity anyway.