Personal theory: Possibly the Great Attractor has something to do with a very large collection of dark matter - potentially dark matter galaxies. Hard to say though until we figure out how to see that section of space.
There no reason to believe dark matter had anything to do with the Great Attractor, it's just that we can't see it due to it being on the other side of the galaxy what makes it great
Read into it. Large amounts of dark matter fall into the one of several theories presented by the professionals as what could be causing the phenomenon.