I've never understood why people do that. The ones you posted aren't so horrid. Its the two hairs thin and arched like a circus clown look that makes me die a little on the inside.
About yey thin, but far more horribly wrong: link
I don't know if Marlene Dietrich is what they were shooting for, but if you're going to do that, ya better look and rock the Old Hollywood look.
Honestly, I've never touched my brows since the 7th grade incident with the razor... Mine are so light any removed hairs is a tragic loss.