This suggestion/complaint sorta reminds me of the problem some folks had with Epona having a "carrot meter" in the older LoZ games. Yes there's no REAL reason to restrict the speed boost just as there's no REAL reason to limit how long we can keep our birds out, but it's a mechanic that can help some other people get a slight sense of immersion (yes the horse/chocobo isn't real and doesn't NEED rest/food but having that limitation mimics a real world thing) basically along with whatever potential backend stuff or gilsink justification. At least that's how I see it.