Why don't referees wear black lines under their eyes?

Answer 1

The black lines under the eye is to allow players who need to cut glare from overhead light. Receivers or outfielders, for example, often need to look up to aquire an incoming ball against the sky. Glare from sunlight or field lights can occur when it is partially reflected from the top of a cheekbone. Wearing a matte black makeup or adhesive material will absorb and scatter the light reducing glare. Since referees, umpires, and other field officials rarely need to watch the ball in flight, there is little need to cut glare. Their gazes are usually on the player activity and the field itself.