[jeffcutsinger]

It's also been shown that when they do ask for higher salaries or raises, they are perceived in a negative light whereas men who do so are perceived in a positive light.

So they don't ask because if they did it would harm them.

[chacham15]

This is not true, women tend to do better when they do negotiate: "However, when we explicitly mention the possibility that wages are negotiable, this difference disappears, and even tends to reverse"[1].

[1]http://www.nber.org/papers/w18511