This is a good question. I think it is fairly clear that gravitational attraction will tend to pull objects into larger conglomerations and that these, in turn, will mutually attract. The motion of these conglomerated bodies will not have zero momentum or zero angular momentum, in general, and so tend to be divided into parts that be in a mutual dance of complex motion under the influence of gravity. I think it is not at all obvious why this arrangement settles down into a disk with a large central core. This is true of solar systems or galaxies. I think it does so, and there are computer models that show this to be the case even with just Newtonian physics, but I don't think the maths is easy to solve analytically. Does anyone know of an analytical proof?
I guess this is the lowest energy state and I can imagine mechanisms that would gradually weed out the counter-rotating (or perpendicularly rotating) bodies but it does not seem obvious. I guess that the large central core is a likely outcome but stating this is far from being a convincing proof.