Because any advice Dinobot sent Primal's way went against Maximal ethics. Primal wanted to capture the Preds and get them back to Cybertron to account for their crimes, not destroy them all as Dinobot often suggested.
Well it would have made for a crummy series finale if he did. Also, Im pretty sure re-enacting the whole "I let him go" scene from Commando wouldn't go over so great in a kids cartoon.