It might have something to do with the fact that, if May went, the widely-flagged Brexiter dream team includes Johnson as PM and Rees-Mogg Chancellor.
Brexit has always been a proxy for Conservative factional wars. It’s just a shame they had to involve the rest of the country.
Here’s what Rees-Mogg thought when he didn’t have an improved shot at a top job:
“[May’s] Brexit deal is dreadful,” he said.
“[It’s] not a proper Brexit. Nothing is going to be worse than what we’re being offered.”
“It’s not so much the vassal state any more, it’s the slave state… this is not Brexit, this is a failure of government policy, it needs to be rejected.”
“We’re on the verge of making a historic mistake,” he has said. “[The deal] is utterly unacceptable to anyone who believes in democracy.
“We have wrapped a suicide vest around our constitution and handed the detonator to Brussels… it is time to scrap [the deal], otherwise we should tell [the EU] they won’t get a penny.”
But never mind. Because now Theresa May has promised to quit if her deal wins enough support, and ambition beckons.
To be fair, Rees-Mogg announced his change of mind a few days ago when it was only heavily speculated, rather than a certainty that May would offer her head on a plate in exchange.
He said his preferred option, a “no deal” Brexit, was no longer a foreseeable outcome, and in the end he wanted some sort of Brexit rather than no Brexit.
It’s a fair argument. But May’s deal has been the most Brexity Brexit option that Brexiters could reasonably hope for a while, and yet Rees-Mogg somehow didn’t realise it.
There’s not a huge amount of difference between no-deal being the default option on March 29 and it being the default option on April 12. But that fortnight somehow became an eternity when promotion beckoned.
Whatever the actual motive of these two and the other MPs who have changed their mind thanks to May falling on her sword, their apparent motive means they have bitterly disappointed the hardline Brexit wing of the Conservatives where they’d made their habitat and gathered their allies.
When Brexiters reveal they’ll vote for Brexit, they lose their Brexit cred.
Rees-Mogg, absurd Blackadder caricature of a born-to-rule Tory he may be, had a reputation for integrity. He presented himself as a man utterly bound by convention and history, a message reinforced through clothing, accent, and a habit of quoting obscure centuries-old political anecdotes.
He may still talk his way out of this with a handy 17th century precedent, but his brand is heavily tarnished.
It would be generous to a fault to say Johnson had a reputation for integrity, but he had authored the most flamboyant and well-remunerated attacks on Theresa May since quitting her Cabinet, using his media pulpits to pepper her and her plan with regular scorn.
To back down so quickly with barely a warning is already being seen in some Brexiter corners as an extraordinary betrayal, a “reverse ferret” of truly tabloid proportions.
But Brexit has always been a proxy for Conservative factional wars. It’s just a shame they had to involve the rest of the country.
The extra irony is that it could easily be for nothing.
Theresa May saw a chance to get the Brexit she has fought for (after campaigning for Remain), the flawed but acceptable compromise she has heroically, repeatedly insisted the country put up with, a living, wheezing sunk cost fallacy of a Brexit.
She threw herself to the English lions, in the hope that her Brexit could sneak out to freedom during the slaughter.
But there is a rump of Brexiters for whom compromise is the enemy of patriotism and who will resist May’s Brexit to the last, because it’s not their Brexit (recall the many republicans who voted against Australia becoming a republic in 1999).
And there is the Northern Irish DUP, who don’t see any advantage in a new PM, and who still sweat in fear that the May divorce deal could lead to a united Ireland by mistake.
And there is John Bercow, the Commons speaker threatening to kill May’s chance at another vote on the deal on a point of ancient precedent, enforced when so many others are being blithely binned.
To win that vote, and successfully lose her job, May probably needs the help of quite a few Labour MPs.
You couldn’t make this stuff up.
And this show isn’t done yet.
Nick Miller is Europe correspondent for The Sydney Morning Herald and The Age