If I was to guess I'd say the purpose is to establish familiarity.. assuming this community migrated during the great reddit migration.. also i think it looks cool so..
But it's partly cut off... And the banner is just the logo, but stretched so far that it's completely jpegged... How can that possibly look good in any unironic way? .___.
Ideally the logo should be something simple, because it gets displayed in many different places and usually pretty small. ~500x500px should be enough, and the main content should be inside a circle, because the corners are often not displayed.
A more detailed artwork is better for the bigger banner. Most communities seem to use something around 2000x1000px or so.