Because there was nobody to vote for who offered that. McCain's proposal was to deny that the problem existed. Obama's proposal was Obamacare without an individual mandate. Clinton's proposal was Obamacare with an individual mandate. Those were the only entrees on the proverbial menu. No candidate ran on a public option, so you couldn't vote for that even if you desperately wanted to.
Ironically, one of the first moves of the candidate who got the most votes, Obama, was to decide that Hillary Clinton had been right after all and include an individual mandate. So if you voted for him over her because you opposed that idea, you were officially SOL.