The additional 15% increase in settler speed was added pre-release. It was probably meant to change something in the economy, but 6.25% isn’t that much. And you need to spend two whole cards for this.
Jokes aside: i think its more of an earlygame bonus → decreasing the time between mines further out on the map and more importantly to run away from and survive raids
Edit: regarding card investment: i would take ‘marco polo’ anyway, the vill speed is just a nice side effect