Because no other race has anything compareable to how godly this is. A player who is not a moron, can easily remove his or her squad from harms way so effectively and efficiently.
All FoF should do is give all Eldar units a passive NOTICEABLE speed boost. Kind of like how fast the Arcon is.
Eldar has always been too powerful of an army, and it's time to balance them.
Either this, or just cut down the HP each unit has for balance sake.