I can see why daggers could be used underwater, they are small and some divers and fishermen do use knives underwater iirc.

I miss fighting bosses such as Emerald Weapon (FF7) in an underwater environment

I would have been glad just to fight the giant mudcrab.

I'll just quote Todd Howard:

"We can do anything, we just can't do everything".

If a game is ever to be released in a reasonable timeframe and at a certain quality level, compromises have to be made as to what to focus on. In Skyrim's case, underwater combat didn't make the cut. They decided to focus on other things instead.

I don't want that for Skyrim. I don't really care even. It was just a general consideration.