My reasons are simple - it's because I'm not done developing them yet to show them on dA. I actually have tons of OCs but I don't have the balls the size of Florida to present those ones, mainly because they're Mary-Sues and/or I feel like they're not all that interesting.
Currently the only OC I have ever put on dA is Daniel, but he's not fully completed yet to properly present in a journal entry. I still have some important things to add to him, and I'm planning to do a redo drawing of this: It's damn ugly, but I can't delete because I had the longest comment roleplay on that deviation, and I only like it because of that. (If you want to see it, go check Daniel out now).
[Oh, and (my friend on this site), I also want to publicly ask if you have any OCs you'd like to discuss and download on dA. Tell me in the comments!]