"There’s one Democrat who would seem to have little or no chance of being picked by Sen. Barack Obama (D-Ill.) to be his running mate – his former opponent, Sen. Hillary Rodham Clinton (D-N.Y.). But it’s not for the reason you think. Obama has often said, most recently on NBC’s “Meet the Press” on July 27, that Clinton “would be on anybody’s short list.” But apparently not his. “She was never vetted,” a Democratic official reported. “She was not asked for a single piece of paper. She and Senator Obama have never had a single conversation about it. How would he know if she’d take it?” The official also said Clinton never met with Obama’s vetting team of Eric Holder and Caroline Kennedy. And the official said she was never asked for medical records or for any financial 2008 information about her or former President Bill Clinton. The Clintons also were not asked about donors to the William J. Clinton Presidential Library."
And there's another reason why the Clintons weren't picked--fear of more Clinton scandals.