My three top theories (in no particular order):

1. She is sick of it (any real human being would be).
2. She is taking herself out of contention (for president) for the good of the GOP.
3. She is going to run for President of the United States of America.

I for one plan on retiring from business (successfully) in a few years and becoming, first a fund-raiser for Sarah, and then a speech writer. I look forward to working in Washington.