But, as Seraphor said, that's the point. If there were no charges it would be worse because you would have to use them exactly when they finish cooling down, every time, to maximize their damage contribution and you would never use them for the movement. Giving them charges lets you actually use them for the movement if you need to.
That's some strange reasoning, considering rangers are the most mobile role in the game even without movement actions, and they would be the least inconvenienced by having to use movement actions on cooldown for their damage.