I think - so far, no one has managed to work out just what is going on, and how we got from the start to where we are now - the numbers are wrong for how the universe is unfolding.

I have to confess to a certain wicked satisfaction over this difficulty.

When the galaxies are studied, quantified and their velocity and acceleration calculated insufficient mass is visible to account for the way they move.
Basically, they aren't shiny enough.

\I think that galaxies have to have formed first.
At the start, everywhere and everything was all in the same place, and then there was light.
At first there wasn't light because there was nowhere for it to be, or do its thing.
Nothing could happen because there was nowhere for anything to happen, so probably time could not go either.
Then - bang - as they say, and everything was up and running away from everything else, and matter separated into smaller bits and gravity began to make the spaces between the bits larger, so there were galaxies, and then began the great dance where there was movement and meetings, and the term orbit became interesting.