Because it's very close to what many athletic women weigh. Not really that hard to grasp.
Which athletic women? From what I'm seeing female athletes at 5'7" weight around 130 lbs
http://www.wnba.com/playerfile/samantha_prahalis/
http://sports.yahoo.com/olympics/soccer/alex-morgan-1131355/
http://www.wnba.com/playerfile/becky_hammon/
If one just cares about aesthetics only, why care about how much you weigh? Isn't the goal to look good regardless of how much you weigh?
My thoughts anyway. I can understand wanting to reach lets say 175 @ 12% bf because you once weighed 190 and are trying to cut down. But to say specifically, I want to way this much, never made any sense.
If my logic makes any sense lol.
I care nothing for numbers. I'm just saying that I'm not a power lifter, who is 5'7" and will weigh likely in the 165 range when cut and I think I look fine. I'd pay attention to my weight if I competed.