I am not a big defender of this idea but I can guess an answer to your question: the regularity of the extinction events suggests a regular disruptive force.
“I am not a big defender of this idea but I can guess an answer to your question: the regularity of the extinction events suggests a regular disruptive force.”
Agreed. However regular and predictable events in the cosmos are the norm, even if they take place on a scale of millions of years. No need to bring Dark Matter into it.