I guess it depends more on the type of protagonist. I would expect someone who has woken up from being dead for a while with no memory whatsoever to be questioning why on many things, as currently they are just told to jump, and so they listen. I can't see it that difficult to record 20 min of dialogue (3 per character in relation to their origins and another 8 scattered throughout the game's path) to give context to the game itself. Especially with the amount of money invested into this game (the 500 mil throughout the 10 year Activision publishing contract) It seems so wrong when comparing the game to Bungie's past titles which actually gave context, meaning, and reasoning to your own actions.