The aliens arrived in secret and hide on the blue side of the moon. And as they scanned our internet, they decided that Felis catus is the dominant species on Earth, as Homo sapiens sapiens clearly does their bidding all the time.
Now, the aliens do have some odd streak in that they seek out other planets to find a worthy overlord, and they believe this time they might have managed it!
Now, their search for the perfect overlord species to themselves prevents them to ever discuss terms with other subservient species, which means they can't contact humanity - even the idea of trying to decipher the language and glyphs humans use to describe things are so alien to them that they will not do so. They also can't just abduct any member of the overlord species Felis catus, because that would be sacrilege and even thinking about it makes them commit suicide. They can't pass for humans even passingly as they are Starfish Aliens of truly non-humanoid design. They can't also just use an invisibility technology or psi, as such doesn't exist.
How might the aliens still get in contact with a representative cat? Of course, eradicating humans would be a way to not need to contact humans, but glassing the surface also burns Felis catus.