Because there aren't enough of us.
And possibly because we are hiding from our current manuscripts (yes, that's plural). I mean, we're writers. We should be writing them, not this. So, what better way to hide an author than in words? It's time to play "find the author in the word-stack."
But for a serious moment, there aren't enough authors. Sure, maybe an author who is currently sending out hundreds of manuscripts and being rejected every time with pathetic "Thanks for considering us" and "Unfortunately, this is not what we are looking for, try again" is feeling that this is not so. Maybe that said author wishes he or she were the only author in the world, then all the publishers would have to accept his or her work. No, then all the publishers would be scrambling over each other, vying for her work, instead of the other way around.
But ignore all that. I'm talking about the general, everyday author who sits at home, antisocial, and writes. There aren't enough of us. We get lonely talking to the computer, the journal, or whatever writing tool we use, and talking to any non-writer, even the best of friends, wins us blank looks. They don't understand, and I don't blame them. I'm quite confident they receive a similar look from me when they begin talking about volleyball or basketball, training sessions or all-day competitions. Here's the thing - there are plenty of other people who they can talk to about said volleyball or basketball, training sessions or all-day competitions. We authors get no one. Or, if we're lucky, one person. Or, if we're very cunning, a whole internet's worth of persons.
Here's to not relying on luck.