The different shapes of galaxies can be easily explained if you understand the major component of galaxies is plasma, which is a charged conductor of electromagnetism.
All of the observed shapes of galaxies can be produced on a miniature scale simply by manipulating electrical currents running through plasma in a laboratory. The three main factors that determine what shape will result are a) the number of electrical current filaments passing through the plasma, b) the plasma density of the regions that the currents pass through, and c) the passage of time.
so why do most of them look like water spiraling down a drain?