The speculation that Theresa May is perilously close to the 48 letters required for a confidence vote has – as Steerpike documents here – been going on for some time. That's not to say it won't happen. Morale is at low point within the party. But as a consequence of that, the sheer number of downcast MPs means that if May's critics really wanted a confidence vote this week they could make it happen.
There are over 48 MPs unhappy with May's leadership – and who think the party would be better off with a new leader. For example, the StandUp4Brexit campaign group alone has now had 50 MPs publicly sign up – meaning they all oppose Chequers:
Not everyone in this group thinks that now is the time to oust May. A handful think that they can still get May to change her Brexit position. But take into account the angered Remain-ers wanting a second referendum and the downcast Tory MPs who are annoyed at May's lack of domestic agenda and it's quite easy to see how you'd get to over 48. As for speculation that Graham Brady isn't being entirely honest with his arithmetic – few believe that is really case. And even if it was, Tories could simple send 15 letters at once in simultaneously in order to ensure it happened/couldn't be ignored.
So, why hasn't a vote happened? To put it simply, May's critics still aren't sure they have the numbers to win it. Speaking to MPs in recent days – both in the Conservative party and DUP sources – it's clear that the greater concern is what would happen if they made a move against May and then she survived that vote. If May won the vote, she would be immune from challenge for a whole year and you could begin to imagine a scenario by which May survives – Amber Rudd and her fellow Remain-minded colleagues flock to College Green, where they quickly tell any broadcaster who will listen that May has seen off her rebels and should now go the whole hog to a soft Brexit – with a customs union and single market. With the Brexiteer MPs out, they say that this is the only way to win enough support to get a deal through Parliament.
It would allow May the space to manoeuvre to an even softer Brexit. One that would win the support of a lot of Labour MPs, even if it turned a large chunk of her party, and the population, against her. May would also know that with a third of her MPs voting against her, her time as leader was coming to an end anyway, and so would be less reluctant to rely on Labour votes to get a deal through. This would be the Brexiteers' worst nightmare – and is the reason why for the time being any confidence vote will be cock-up rather than conspiracy.