Me and my girlfriend despise babies (for now) and simply don't see ourselves as being responsible/mature enough to raise kids yet. We do entertain the idea though, now and then, and for us the main attractions of having kids seem to be: Something we made together, a "substitute" of each other to live for after one of us dies, and something to carry on our legacy, such as it is.
With adoption, these things can be fulfilled if the child is young enough, to be molded into our image, as it were.
That's not to say that love for an orphan, no matter how old, cannot happen. Of course there can be selfless adoptions, where you just want to make someone's life better without regard to yourselves.