User blog comment:One Of Terraria's Best/My Main Question/@comment-25406792-20140911013139/@comment-24197468-20140918233900

Open software would indeed be a horrible idea. There is no way the developer could fund the process of keeping it up to date and clearing all the bugs. It would also give the entire world acces to every detail of the game making it really, and i mean reeeaaaallllly easy to make replica's of the game with just a small twitch to it, making them loose money in the precess of not elling an own copie.