The Marker signal doesn’t just reanimate the dead. It manipulates us into spreading the Markers. And now we too have been unwittingly spreading this galactic virus from planet to planet. The propagation of our species has only served to create a source of food and the means of finding it for those these moon-sized entities.
It is no wonder Tau Volantis chose self-sacrifice. They eliminated themselves like a gangrenous limb, hoping to keep the infection from spreading to us.