.
A lot of it had to do with the fact that they were positioned on the lowermost wall of the
fortress which was basically the front line where the main attack was going to come strongest right away. As where the
men of
Rohan were high up on the keep and didn't get stormed by the enemy until after all the
elves had died protecting them. They were the first line of defence and they were so greatly out numbered that the urukahi just plowed them over.
Secondly they are not the great
race they used to be as far as the lands of
middle earth are concerned, they were forgiven by the
valar and all had the option to pass into the west. Most of the elves that comprised their great
armies of old were already gone and those who fought at
helms deep were more gaurdians of the remaining dwellings of elves. I guess what I'm trying to say is they didn't have the same fighting spirit as they did in the past because they didn't need it. They did not have to fight for their right to live in the world, they could just take the easy way out and take a ship into the west. Ultimately, they didn't
have to be there.