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The Earth was created from the same stuff. The earth was created from the debris from a supernova explosion.

"Then shouldn't they be out at the 'edges' of the Universe instead of mixed in willy nilly?"

Here's how to think about that. In the beginning, the whole universe was all at a point, or tiny area. The stuff didn't fly out from there, space expanded. It's the space that is doing the expansion, not the stuff. That means, as you look out into space, the things you see, are things that were happening distance/c years ago. The universe looks like a balloon. It is all contained in the surface region of an expanding space-the balloon surface. The speed of light restricts how much of that surface region we can see. It is really quite small, and looks flat from here. If you take a balloon and make 3, or more dots an it, then watch the dots as the baloon is inflated, you'll note that they always get further away from each other.

The universe is expanding at around c. C is usually used for the expansion rate. So it's the balloon's radius that's increasing at c. The surface of the balloon just gets a bit thicker as time goes on.

As far as the edges of the universe go, they are in the future, so they can't be seen, only the past can be seen and it's all in that balloon like surface.

Ok, just refreshed about the clusters. They were formed a very long time ago from stuff that was relatively dense and close in, so things flying in from elsewhere to impart spin didn't occur. They have a very nigh density of stars and either a black hole(s), or bunches of neutron stars in the center. They are the first objects to collect and form spiral galaxies, such as the Milky Way.

It's quite easy for me to see that as an object like this formed from high density stuff, it collected the orbiting WIMPs and now the fog that appears, is simply the gazillions if complex and ever changing orbits in the cluster. The stars do the same complex orbits, because they're always being purturbed by nearby passing stars, but they're moving slower and can collide. Being an old system though, collisions will be rare, because the orbital paths are relatively stabilized. The axions however just whip through the stars and see little gravity bumps. Gazillions of them can orbit a central black hole, as if the other stars weren't even there.

Things inside a large spherical mass only see the gravity of the mass inside the radius that is equal to the distance of the thing from the center of the entire spherical mass. So the axions are simply orbiting the huge mass in the center. There's high order effects in gravity which result in fine structure. Those and the fact that the field comes from many objects give the gravitational field of the cluster a multipolar configuration. That can be seen in the image above on the thread as the regularly placed and appearing lumps in the pic. So,I'd say the fog of dark matter in these clusters is simply due to the orbits.

the analogy is the electron cloud surrounding the nucleus in any atom, or molecule. The particle orbits, but is observed as aa cloud. That's because, as the electron goes through it's various orbits, at relativistic speeds, the fog density follows where the electron most often is.