I phrased that poorly. It's more that the automatic link between settlements that the Caravan Plots make between each other has that finite range. You can, of course, set up a "chain" of settlements - you can get every base game settlement linked together in that way.
For example. I often do Sanctuary -> Tenpines -> Taffington -> Mechanists -> Castle - this way, despite the link only being roughly the distance of Sanctuary to Tenpines, even at the Castle I can access Sanctuary's resources.