Resources.
Yes, resources. I’m surprised at the arrogance of those who believe aliens with the resources necessary to visit our planet would find this mudball worth expending the resources to do so.
The Earth is less than a tiny speck in the Universe. How many resources do we hold?
If an alien species can travel through the Universe, they control massive sources of energy. They can transmute metals; turn gold into lead if that's the resource they need. If the need water, they can make it form oxygen and hydrogen.
Astrophysicist tell us there are planets that rain diamonds and asteroids made of pure gold. There are more abundant sources than the Earth.
Our resources are nothing on the scale of the Universe.