It would have been awesome and would have made sense. An Imperial crossbowman would be pretty bad ass. They were in Morrowind and also in Skyrim with the dlc. I think that this weapon should always be a necessity in any elder scrolls game, but thats on a different note.

So why do u think they never added it in?

I blame it on 11/11/11.

No, but seriously. There are several weapons missing from previous games, such as spears and throwing weapons. I don't know why they were removed.