Why are most Tory MPs so quiet over partygate?

At the beginning of the year, letters from Conservative MPs looked to be reaching the 54 threshold needed to trigger a no-confidence vote in Boris Johnson. Most would think a fixed penalty notice from the Met would bring us at least back to those levels. And though there have been some full-throated calls of support and condemnation of his leadership from his parliamentary party, the majority have remained conspicuously quiet. 

James Forsyth asks Katy Balls and Fraser Nelson why?