Shiv is a moron
Her ego and just constant need to not give Tom anything is exactly why their plan failed
He legit called her and asked her what his position would be and she was juelzing like usual. Did she not think he couldn't mess up things for her?
In fact if we go by the beginning of this season up to this point Kendall wanted to do this same play and they all told him no they stood a better shot at sticking with Logan
Now they have all been firmly pushed out of power and are shocked
except kendall because he already knew this move was coming
You could make an argument that Kendall helped push Tom to this outcome based on their diner scene. At least he was smart enough to see Toms value unlike Shiv but he definitely planted the seed that Shiv don’t love him and they all know it.