Why do football players put black lines under their eyes?

Watching parts of the football games this weekend reminded me of the black lines or smudges that many of the players put under their eyes.  I had always "known" that this helped to reduce glare in the eyes but I wanted to check and see if this was true and how much it actually helped.

I found that this grease is called eye black and players in baseball and football have been wearing it for some time.  In football it dates back to at least 1942, it goes even farther back in baseball and was originally made from burned cork ashes.  The glare reducing effects hadn't really been tested over the years and over time eye black has been used for the intimidation factor and even as a message board.  Advertisements and other messages can be seen on some players with commercial eye black stickers.

A couple of studies were done within the last ten years and it was found that eye black gives a "small, but statistically significant" increase in glare reduction and contrast sensitivity.  Interestingly commercial stickers were found to have no advantage over petroleum jelly, the control.  One of the studies found that eye black was less effective on blue-eyed people, likely because they have less pigment to block out the light.

So it may give some benefit, but it seems like most players simply do it for the ritual and the "fashion".  And if it could possibly give a small competitive advantage then why not?