Why did anyone wear horns on their helmets? … Why did so many other professional warriors risk their necks by attaching horns, wings, small animal effigies, horse tails and other doo-dads to their helmets?
Never underestimate the need for symbolism over pure functionality. Boar crests are thought to have symbolised strength and aggression, and may have been thought to give the wearer that strength and aggression. Some decorated helmet plates are thought to have had an intended apotropaic effect. Perhaps wings and other protruberances did the same, or are about status and rank instead. When face to face and hand to hand with your enemy, the need to look impressive and to cow them may have trumped pure functionality.
The NSFW webcomic “Oglaf” explains this quite well, actually…
We get slapped around, but we have a good time!