system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are galaxies shaped like disks and are there any that are not?
gpt
There are many, many galaxies that are not disc shaped.  For example, elliptical and irregular galaxies.

There is still a great deal to be learned about how spiral galaxies form.  Generally, the disc shape is a result of rotation--a galaxy can be roughly though of as a bunch of matter orbiting a super dense center, containing a black hole.  This orbit sometimes tends to align itself on a single plane, and so you get a disc shape.