But that's not the reason, says New York Magazine. The real reason is that he was leaning Obama, but Obama blew it:
According to a Democratic strategist unaligned with any campaign but with knowledge of the situation gleaned from all three camps, the answer is simple: Obama blew it. Speaking to Edwards on the day he exited the race, Obama came across as glib and aloof. His response to Edwards's imprecations that he make poverty a central part of his agenda was shallow, perfunctory, pat. Clinton, by contrast, engaged Edwards in a lengthy policy discussion. Her affect was solicitous and respectful. When Clinton met Edwards face-to-face in North Carolina ten days later, her approach continued to impress; she even made headway with Elizabeth. Whereas in his Edwards sit-down, Obama dug himself in deeper, getting into a fight with Elizabeth about health care, insisting that his plan is universal (a position she considers a crock), high-handedly criticizing Clinton's plan (and by extension Edwards's) for its insurance mandate.That's actually pretty damning. One hears stories about how gracious and charming Hillary can be in a one-on-one meeting, even if that charm doesn't carry over during big speeches. Is Obama disadvantaged in the other direction? Is he great with the big crowds but clumsy in person?