That does make sense. There is a difference, like Reena said above, about working backwards. If you just accept the ship and then ask what that says about the character you might get a different answer than starting with the question of "Who is the best girl for X?"

I do think people probably also just prefer any story where they feel involved in the developments rather than just being told. In romances there's usually so much care put into making the audience root for the couple, and in other stories there really isn't. That doesn't always ruin the story, but it can detract from somebody's enjoyment of it if they want to root for them or at least feel something more when they finally get together.