Well for one thing, no matter what they didn't they couldn't make everyone happy. There are enough people who think their NElf's is a bodacious babe like TERA elves, and there are enough who think they are tough amazonian warrior women that if Blizzard made them one or the other, the other side wouldn't be happy. As it stands, the "old" models are so non-descript and poorly detailed that they can be almost anything. Young, old, tough, svelte, whatever.
What it comes down to is the fact that Blizzard isn't asking you what you do or do not want changed. They're attempting to make their models better represent the style that Blizzard first imagined them in, but that poor graphics technology would not allow them to create.
People are taking this damn model too change WAY too fucking personally.