Because then you have to choose between protecting yourself vs. iron (via punishing them for it with shield of electricity) or protecting yourself against lag, which could turn your 2 round nukes into 3 or 4 round nukes or even potentially just flat out permalag.
If you are, say, dark elf fighting mostly fort types, you can probably deal (relatively) easily with the metal vuln. They don't tend to have many of the lagging types. If you are, on the other hand, fighting mostly rager types, giving up prot vs. cranial could be a recipe for disaster. As a high elf, that equation boils down to what is in Empire at the moment, which can always change and potentially quickly.
I'm not saying elf/d-elf is unplayable, far from it, but if you want easy pk's that isn't where it is at (human) and if you want easy choice, you probably go arial (always flying, always covering vulns, just decide what shield gives you the best options), but elf brings added complexity which could help or hurt, depending on how well you handle that.