The real question is "why not?". Yes it could go to mars, but why go through the trouble when there's all those juicy resources right here? But even so, when it's done with the other planets, why not come back to Earth? Why not build a Dyson sphere to absorb the sun's energy? Oh, we'll stop it? Yeah, another reason to wipe us out to begin with.

Why not is a surprisingly difficult question to answer, and it comes down to 'care about what humans care about' which is itself unbelievably hard to pin down.