Because being on the receiving end of a public broadcast does not give you the right to re-use the content. The content owner, for better or worse, typically retains the exclusive right to use or broadcast the content, regardless of how many times it is broadcast.
Consider older mediums; does broadcasting a TV show put it into the public domain? Or playing a song on the radio?
> Consider older mediums; does broadcasting a TV show put it into the public domain? Or playing a song on the radio?
In a sense, it does, yeah. It's just that copyright injects a century or so of lag time before members of the public domain are allowed to exercise their rights.
Consider older mediums; does broadcasting a TV show put it into the public domain? Or playing a song on the radio?