Revenge on who? The guy who helped him against the big bad who orchestrated the whole thing? Guy's already gone. He needs a companion and that's it. Ganondorf was just following the command of a big guy who he attacked when it was found out he was controlling someone he wanted to work for. Ganondorf's still a jerk, but he's not even close to a true bad guy in this game. He decided to help the heroes. There's little point in taking revenge on him.
Ganondorf wasn't forced to obey, "master hand", but through circumstances, he did anyway, knowing he would be harming the many ROBs of the Floating Island. He pressed the button in which would activate total control over the ROBs. He pressed the button that commanded those ROBs to attack the one ROB who stood up for his land and his people- all while said ROB watched. Not Tabuu- Ganondorf.
Of course, Ganondorf is still considered evil so he could easily justify it(and I have a feeling Ganondorf helps the good guys in the actual story is probably why R.O.B. decided not to go after him, because it was truly Tabuu that was response for the death of his friends. Ganondorf and himself played a role, but not to the same degree). Also, I don't know if R.O.B. even knew about Tabuu as is. If he did, that's the only one he wanted to go after. I have a feeling he still would easily hate Ganondorf, but he's also a robot. He goes by logic. Ganondorf was probably following orders, so he may not have wanted to do it at all.
Logically, he wouldn't have tried to talk to his friends while many bombs were set to blow nearby. He had to be dragged off by Donkey Kong so that they could escape. Just because he's a robot doesn't mean he follows complete logic. See Johnny Five.
Mind you, I forget if Ganondorf does this before or after he finds out about Tabuu. Either way, I think R.O.B. going after Ganondorf, who helped the heroes, isn't logical for a robot to do so. Finding someone to help him get through this makes more sense.
Since when is that true ever? (Read above)