Why? In part it is because Miliband fails the greatest test for a leader of the opposition: you cannot imagine him as prime minister.
And in part it is because of his flawed campaigning since 2010. Even if you agree with them that the Conservatives and the Liberal Demcocrats are evil, you still want to know what Labour would do differently. And of that we have little idea.
But above all the greater electability of Johnson is a mark of the self-defeating hegemony of the political class. (I realise this post lacks a definition of that class, but they are much like elephants - you know one when you see one.)
Ed Miliband's c.v. - adviser to Gordon Brown, cabinet minister, party leader - is at once the ideal of that class and a guarantee that he will have little appeal to anyone else.
This should not be such a surprise. Fairly or not, the two most prominent members of this class within Blair's inner circle were also its two members most disliked by the public. Step forward Peter Mandelson and Alastair Campbell.
Meanwule Alan Johnson has had a life outside this class - as a failed musician, postman and trade union leader. That almost in itself is enough to make him more appealing than most politicians.
Perhaps this view of the political class is unfair - perhaps things were always like this. Certainly, there were plenty of political dynasties in the past. But this modern distrust of professional politicians is widely entertained, and the attitudes of many young politicos does nothing to discourage it.
I doubt Labour will find a way of making him leader, but they would have a much better chance at the next election if they did.