@YetAnotherBrony
Part of it is aesthetics. If a large population of a species finds a specific trait attractive, that trait (in theory) will become more prominent. One great example of that is the peafowl. The females of the species found large, elaborate tail displays attractive. As a result, large, elaborate tails in males became more prominent.
@Prof.NightJack
If the artist has more than one name, then the mods will usually just pick one to use here for their tag, and have all their other names be used as aliases which will autocorrect into the chosen name.