New York, New Hampshire, New Jersey, New Mexico.
People like to name places for the ones that they formerly knew.
The rivers spoken of "encompassed" lands that were part of a single land mass, prior to the days of Peleg (when the earth Split.)
After the flood, when Noah's posterity was scattering on the earth, they used the names of places that had been theretofore known. Hence, the rivers Euphrates and Hiddekel.
That is my theory, anyway.
Walt
(By the way, the expression "from the rivers to the ends of the earth" I believe to be a summary of all of the whole land - "The Rivers" being the location of the fountain that split into four heads, and "the ends of the earth" being - well - the distant shorelines.)