For 99.9% of all possible goals it might be interested in accomplishing, more resources are better than less.
If it has any interest in spreading all over the galaxy, that same interest will first spread it all over the Earth. If it's concerned about the heat death of the universe then its best course of action is to build a Dyson sphere around the sun, sooner rather than later, and that requires a lot of atoms, which the Earth is a good source of.
And if it's worried about a more efficient AI wiping it out, its best course of action is to wipe out the humans, who have demonstrated a tendency to create AIs.
If it has any interest in spreading all over the galaxy, that same interest will first spread it all over the Earth. If it's concerned about the heat death of the universe then its best course of action is to build a Dyson sphere around the sun, sooner rather than later, and that requires a lot of atoms, which the Earth is a good source of.
And if it's worried about a more efficient AI wiping it out, its best course of action is to wipe out the humans, who have demonstrated a tendency to create AIs.