Vast distances prevent panspermia. Think about it vice versa, the consequences of life being able to traverse interstellar distances would be devastating. WE EXIST because it is impossible. Otherwise we would be wiped out by competing alien species. Inevitably, there would only be one dominant species in the universe. So there are multiple lines of reasoning leading to the same conclusion.

It also suggests that the universe may support multiple intelligent lifeforms, each dominant only on its own planet. This idea attributes to the univerese a large scale cellular structure, each system sufficently isolated as to not annihilate its neighbor. Beyond that is gets muddy. But there might be more to it.