Sol Divisive are not under the Witnesses direct control as proven by the Deterministic Chaos mission. They will only work for the Witness if it benefits them. As for the Cabal, there is no major reason why they would not attack. I think part of it is that the major leader or control of the Cabal forces is dead, being Calus and Nezerec respectively. I am really surprised we don’t see Scorn. They, much like the Taken, are mindless forces of direct will and control. There are some forces not under the direct control of the Witness, like that of Fikrul, but the majority are under the Witness.