Anti-vaxers day of reckoning is Nov 24th, page-21

Yeah , not a bad question I thought and maybe it was Dave who was a little "crusty ".
There's still that 10% !
If we had the original COVID , (I mean no mutation), there would have been a good level of herd immunity and very little spread at 90% vacc. but that delta variant hugely more infectious and also some of the other variants but I think delta most common now .
So simple answer , increased transmisability of the delta virus variant .

With 90% will spread slower of course so hospitals much less likely to be overrun .