You really don't need a pre-made license, like one of the Creative Commons licenses. Just grant the use of the speech and recordings of the speech for any purpose. Or make the text of the speech free for noncommercial use.

Why would it have to already exist? Anyone can create a license. Pretty sure some lawyer would've done it for free.

Just about anybody in recorded history could have created the phonograph. It's a dead simple concept, even the Mesopotamians probably could have managed it, all you need is a needle (probably could be bone), something to scratch lines into with it (wax for instance, maybe the clay they used for tablets), and some sort of diaphragm (leather should work nicely). Just imagine, we could have voice recordings of Alexander the Great, or Gautama Buddha.... that would be fucking wild.

Nobody did it until Edison in the late 19th century. Why? Because the idea of doing something is in most cases more elusive than the ability to do so.

Rights were already being sold for printing, delivering, and televising speeches. It would not have been a new idea to license those rights.

The idea is licensing designed to keep a work free, not licensing designed to restrict. Even if that idea existed at the time, it was not prominent, evidenced by the lack of stock licenses to do so at the time.

As you say, "Rights were already being sold".

"I hereby dedicate this to the public domain" would probably have sufficed.