Because it has a small market share. Nobody wants to write a program that will work on unix based systems because it just isn't practical. The main reason for this is that Linux systems vary wildly in terms of operation and security. Windows does not have this "problem" (and lack of standardization is what has kept Linux out of the mainstream) and, to a degree, neither do Macs. Who would want to write a botnet for linux systems? Now, if our dreams become a reality, and Linux becomes the de facto standard then we will have problems too, this is a perfect example of security though obscurity. The opportunity costs outweigh the benefits, as long as this is true then Linux users have little to fear.

If you played this when it first came out you'll probably agree with me that Shodan was an implacable and reactive enemy that would not only threaten you but follow through. And this was all obviously scripted (the best way to create a realistic intelligence, look at how intelligent the NPCs in the Fallout series were compared to your average level of interaction in a RPG). I don't think that an average game developer has the resources to create an amazing AI for just one game leaving simple algorithms + scripting for specialized situations as your best bet to get a realistic feel to the in game situation.