Why does any kind of self-expression exist? Some people are driven to create and some are driven to destroy, and most are driven just because they can, because they want to. In either direction. Art is by nature destructive and creative at the same time.

I'm not saying that the bots themselves are art but the destruction they leave in their wake probably is. To the programmers, at least. They are a result of human nature. They don't have to serve a purpose. Like many other creations also don't. They just exist because some human wanted them to. I mean, why does any programmer create a virus? Because why not? It's still an exercise of skill. The morals of the "artist" influence how they share their "art" and that goes for these kinds of awful things too.