[Why did the moderation edit button have to be right next to the Quote button, dangit]
The qualifications for the Message Board releases are so low and easy to meet. The quality level is bare minimum, especially BECAUSE inexperienced creators can get their content out and learn from feedback. But you need to have showed you at least tried. You also need to meet filename contentions so its clear what a file is for, and what version it is, making things easier to sort through in folders and, far more importantly, keeping everyone in sync during multiplayer.
If you can't meet these goals, then you really aren't trying hard enough. Again, this bar is not hard to clear. The most common reasons for mods to be on GameBanana and not here, is if its a deliberate joke, of such poor quality that the user wouldn't be allowed to let it in, or even the user of the mod being a banned user. Sorting through GameBanana's SRB2 and Kart sections are like sorting through trash to find the half-eaten burger.