Sidious made a lot of promises, first to Trade Federation and Nute Gunray ("I will make it legal", "Not for a Sith"), latter to CIS as a whole. Yet, all of his promises for quick victory turn out to be hollow and unfulfilled.
Finally, we have Separatist Council hiding on Utapau, with their final desperate offensive on Coruscant defeated and Dooku dead. Then they move to Mustafar, and shortly after that Grievous is killed. Yet they still believe Sidious and wait patiently there like sheep to be slaughtered.
Members of the Council supposed to be shrewd and cunning beings, that made it to the top using treachery of their own. Yet, none of them suspect Sidious (although they certainly have some knowledge about the Sith), and none of them tries to strike out on their own. There were not attempts to flee, surrender or negotiate with Republic, bribe their way out etc ... either individually or in group. How could that be explained ?