[Drew68]

Why would an alien want to come to an obscure planet in an obscure galaxy?

Lebensraum. They need the living space and earth is close enough to their home planet that they could terraform it easily enough. Alter the chemical composition of our atmosphere, change our temperature slightly so that our planet would be hospitable to them (and poisonous to us). Replace our plants with theirs, our animals with theirs. They'd have a happy home and we'd have no chance to survive.

[jmcenanly]

With the resources of an entire solar system at their disposal, why would they bother with a dried up rock like this one? There are more resources in the asteroid and Oort belts than on Earth. Even Jupiter's moon Europa has more water than Earth.

It would make more sense for them to simply build habitats than to try to terraform a planet