I think it's because the kind of circles Clinton moved in, she had dealt with a certain level of sexism her whole life, but because she did live that life, she was unprepared for just how much hatred she would receive. Kamala, on the other hand, didn't delude herself into thinking it wasn't going to happen. What I'm surprised about is how little racism she has faced. I expected it to be worst, even among Democrats.
Also I do Kamala is getting just a little bit of a boost because there are some people (women) who realize what a huge mistake they made in not voting for a woman when they had the chance that first time. Sometimes, it's all about timing. The country has undergone some changes that simply didn't exist 8/9 years ago, and Kamala isn't facing the same mood or temperature as in 2016.