It's inseparably tied to deviantart, tumblr, and all the sonic/anime/game fan characters that infest those places. When Stan Lee created Spiderman, he didn't tell everybody to check out his "OC". They're CHARACTERS. There's no reason to emphasize the originality of a character unless you're insecure about how you stole the design from somewhere else. I can't design a character anymore without feeling like some tumblr reject drawing a sonic fan character. It's ruining my good times.
Also there's this egotistical slant on the whole concept where your OC is supposed to represent yourself. Your OC is much cooler looking, more talented, and more attractive than you. It's weird and depressing seeing all these kids pretending to be fictional characters rather than just being themselves. I feel like this is a precursor to the matrix where everyone is an avatar instead of a human being.
