Then, in all honesty, you weren't paying attention.
Under Alaskan state law, the governor is vulnerable to certain legal actions -- but the state could not involve itself in the governor's defense. A number of frivolous suits had been brought, accordingly.
As a private citizen, she had access to the protection of libel laws and could set up a legal defense fund.
Remaining the governor would have driven the Palins into bankruptcy and, at the same time, handcuffed the state's policy machinery.
She caved into extortion.