I cannot say I am surprised that Antonio Conte will pick Nathan Ake over John Terry to replace Gary Cahill.
Terry is vastly more experienced but he would be exposed playing on the left of the back three.
In that position you have to defend more in one against one situations and Ake is a more mobile option.
Tottenham are also more suited to playing with three at the back but in the absence of Danny Rose, Mauricio Pochettino has switched to a back four.