Partially because the amount of money it would take would be enough to upgrade to the current consoles. Can anyone honestly sit here and say that they bought into Destiny thinking it would be on 360 and PS3 for 10 years? Regardless, Bungie has been very careful with how the word things. For example, the Y1 season pass stating it would only contain the first two expansions, nothing else. I highly doubt anyone can find the wording that says destiny and all expansions would be on X360 and PS3.