As Nasyr said, the profile cover is an upgraded user feature that's supposed to look good when someone upgrades. It doesn't change how the forum functions, it has no "p2w" mechanics so non-upgraded users don't miss out on anything. If it looks dull for you, you can upgrade. Avatars can be changed at any time for users, regardless of their rank and I don't think we need default options when a user can upload literally almost anything they want.