I pray it’s not a health issue, for her.
The only thing that changed near the end was that Palin knew the game was up and she would have to admit to her supporters that she wasn't going to run. After teasing it out for so long and generating such a fanatical following, Sarah knew it would be difficult to finally let her adherents down. By not running she also loses much of the media attention she could instantly generate and that is not fun for any politician.
That said, she will help a lot of conservatives raise money and compete in elections in the future. Her endorsement is already being sought by the remaining candidates. I expect her to play a big part in 2012 - particularly at the local and state level.