The most straightforward answer to TPM's question -- Who Killed The Public Option? -- seems to be "the marginal post-Stupak-defection Democratic centrist in the House".
Why is the leadership not pushing for it, when they could pass it a few months ago? Because they lost the most hard-core members of the Stupak bloc, and they have to make up for it with nervous Blue Dogs who don't want to do anything that might sound remotely progressive.
I guess it's conceivable that the perfect effort could get the votes together for it. But in keeping with the Jonathan Bernstein analysis, it would make it harder for us to find enough cooperators to get out of our current prisoner's dilemma, increasing the risk of total failure. I think the risk/reward looks a lot better on the current strategy, especially when you think about the possibility of adding on the public option in years to come.