Because, given the current crop of wannabe hopeless hopefuls, he really is likely to be the best choice as an interim leader while the Labour Party pulls itself together and works out its problems.
Still it is early days. Johnson isn't even a contender yet, and quite likely won't ever be. But given how Burnham and Cooper seem to be hoovering up the nominations of the (pitifully small number) of MPs, it seems unlikely any fresh face can hope to garner enough backing.
Whoever ends up as leader, they need to deal with the myth of overspending. He or she must not be trapped into mealy mouthed condemnation of public spending that was quite justifiable. Labour did not wantonly overspend in the years up to 2008. Labour invested in schools and hospitals and infrastructure to make the lives of British people better. Tories can not attack Labour for this when the George Osborne said, in 2007, his party would match Labour's spending.
Not a word from Osborne then about the need to mend fiscal roofs and austerity. No prophetic warnings about imminent financial apocalypse. Just a pledge to spend as much as Labour, happily demolishing the roof - if you accept his new improved post GFC stance - to let more sunlight in.
Just as Tories can't complain about Labour's failure to adequate regulate the city when the same George Osborne - in 2006 - complained in a letter to the Telegraph about 'burdensome' regultion that 'threatens the global competitiveness of the City of London'
So let us hear no more hypocritical, disingenuous palaver about over-spending when the Tories were pledging to do exactly the same, or about failure to regulate the City when the Tories were arguing the regulations were too onerous.
Or - since the Conservatives will no doubt continue to bleat that chorus like the sheep in Animal Farm - at least let us not hear Labour leaders trying to deny that they over spent. Simply tell it like it was. Labour invested in the means for making Britain a better country and achieved far more than the current government of antediluvian dingbats, Europhobic madpeople, ideologically crippled malcontents and Ken Clarke can ever hope to do.
As for the myth of Conservative confidence, bear in mind the opposing plans to respond to the 2008 crisis. Recall, if you will the Tory pledge to eradicate the deficit in a single term, and contrast Alastair Darling's more measured target of halving it in the same period.
The Tories failed to deliver their planned austerity, though. Osborne failed, but - wittingly or not - DID manage to achieve Alasdair Darling's goal of halving the deficit in 5 years. Which goes to show that the Darling Plan was the sane, sensible and honest one, if you must go down the austerity route. The country is still here, in spite of the right wing howls that Britain could not afford another five years of Labour.
In essence, Britain re-elected the Tories because Labour's plan worked.
Which brings us back to the mess of the Labour leadership. Perhaps the biggest argument against Johnson (other than the fact he's a Blairite relic) is strategic. Cameron will likely seek to repeal the Fixed term Parliaments Act, giving him the choice of when an election is held. he - or his post-EU successor as leader - can then 'go short' and hold an election before his majority is whittled away, rather than hang on Major style in the hope that something will turn up.
So is no guarantee this parliament is going to last five years and allow a successor to emerge to fight in 2020. I imagine the EU referendum will mark the end of Cameron's reign. If he wins, he'll pronounce His Work Here Is Done and resign as PM. If he loses, he'll proclaim a new leader is needed to energise the party. Assuming BoJo or Georgie wins it, they call a snap election if they think they can win, "Too confirm our mandate," rather than making the mistake that Callaghan and Brown did.
So suddenly the 'interim' leader is fighting an election - which Labour will probably lose otherwise the Tories wouldn't call it - and Labour is back in the same situation - carry on with Interim Alan for another three years, or start the whole sorry process again.
Still, even Johnston would be better than Burnham or Cooper.