Carradice: Any hints on why are they taking so long?
Mount & Blade did the impossible: Horses!. Warband improved on it.
Maybe they want to do the impossible again? Not just a better looking M&B but taking it to another level.
They did improve the horses again btw. At least that's what I noticed after watching some of the game's previews. If you were to pay close attention to the way your character stops his horse after doing a turn, the horse doesn't automatically come to a halt as its butt will still revolve around its head for a very short time, making the stop feel a lot more natural. It's tiny details like this that makes me appreciate a game more.
My explanation just now might've confused you as I am not a native English speaker, but I'm sure you'll get what I mean after watching some of the gameplays of Bannerlord that TaleWorlds has so far shown us.