Why do Galaxies form as a circle and not a sphere?

Most of the times when you look at a picture of a galaxy, you see it as a disc/circle thing with a bulge in the middle. Doesn't that seem a bit unnatural to you? Surely the galaxy's gravitational power would affect more then just a small section of the space around it. Right?

One idea I have which is very unlikely. It's that all the galaxies are pointing towards where the big bang occurred/the middle of the universe. The idea being that the big bang exploded and all the debris from the big bang flew of in lines/clumps flying in different directions. So when the gravity pulls all the matter together it forms a disc/circle instead of a sphere. And yes I know that is not logical but I'm just putting it out there.

An other idea which is a lot more likely is that some person has gone along and said these galaxies would look a lot nicer as a disc/circle and everyone has just gone along and copied that person.

The only problem about that idea is that I took a look at a map of our solar system and it looks like a disc/circle too. Apart from Pluto which orbits diagonally around the sun. So unless stars and black holes have an oddity that we don't know about in their gravitational pull, I'm not sure what is causing
this and it looks like we've stumbled across a new and unsolved mystery.

I also think that maybe the disc/circle shape is caused by dark matter pulling and shaping the galaxies and solar systems into a disc/circle shape.

Thank you for reading.

Our solar system

A galaxy

A different picture of a galaxy.