You'd have to ask a political scientist about the "why". I don't really know. But, I do know - or at least every piece of independent polling I've seen - suggests that she has a negative approval rating amongst those two groups. I did see a singular poll - taken just before her resignation - that showed she had a very modest (a point or two) positive national approval ratings amongst independents, but that seemed to erode in a big way after her resignation.
That poll was taken 17 days after she announced she was resigning on July 3, an event that dominated the national news for days and even threw Obama off the front pages. The poll showed Palin at 45/43 (Fav/Unfav) with Independentents. GMAB with your characterization, especially in light of the salting of the sample PPP did in August to eradicate any future chance of a favorable number like that coming out for Sarah Palin.
KellyAnne Conway and Celinda Lake did a bi-partisan poll a few weeks after the election that showed that 64% of ALL women thought Palin got a raw deal from the press.
Independents and particularly women will give her another look. She still has control of her future, as much as it might pain you.