Ahteists must believe that the Dark Matter is the remnants of the God of Atheists (consisting of very special god-particles) - who was the very first Suicide Bomber! He detonated the Big Bang Bomb (presumably attached at his navel, see below) and died starting the universe.
Obviously, this is the best explanation of why the heck they are insisting that he does not exist.
( - and that also explains why, in Hinduism, the universe is emerging from the "Vishnu Navel".)