It IS nonsense. Not sure why they do this.
I bet the associate the brows with getting hit on by guys. But the thing is, when they go out to be picked up, they have everything else going for them "look wise" as well. So they keep up with the drawings thinking it's part of their "sexy look" when in the end, guys just wanna fuck and very few (but me...) will say anything.
I even commented about those brows on my dating profile and saying that women who make duck faces are dumb.
Way to discriminate against 80% of the women on such sites, lol...