Because they published it; they were free not to do so if they didn't want anybody to reproduce or distribute it (in fact that seems like the easiest way to do so).
In order to encourage more people to make these works, however, our government grants them a temporary, limited monopoly on the work's reproduction and distribution, but this is a means to an end that we agree to for utilitarian reasons, not some kind of actual inherent right on their part or responsibility on mine.
> Because they published it; they were free not to do so if they didn't want anybody to reproduce or distribute it
Copyright protects works at the moment they are created, not when they are reproduced or distributed. Most of the works under copyright protection have never been distributed.
Not really, copyright and trade secrets have different subject matter. There are many things could qualify as trade secrets but not creative works (e.g. a recipe), and many things that qualify as creative works but not trade secrets (e.g. a song).
In order to encourage more people to make these works, however, our government grants them a temporary, limited monopoly on the work's reproduction and distribution, but this is a means to an end that we agree to for utilitarian reasons, not some kind of actual inherent right on their part or responsibility on mine.