Stupidity: Wouldn't it be common sense to have more than one remote to control Robo-Cain? That way, if he destroyed one (and he did), they could still use one to shut him down from a distance (as long as they can dodge the gunfire).
Stupidity: Dr Faxx knew full well that Nuke was Cain's greatest weakness, but it never occurred to her to mention to the old man that holding a canister of it in front of him during the exhibition could have serious consequences. Not very bright.
Answer: Just so it would look creepy in the jar (or maybe they thought they were worth keeping, then decided against it). Notice when Robocop pulls Kane's brain out of the 'bot later, the eyes are no longer there.
Grumpy Scot