It's never just one thing, Saddam had to go for the greater israel project, Iraq was getting too strong after the Iranian-Iraqi war. Had scientists and research and wasn't obedient enough (although Saddam was initially propped up by the English, he had to go as he was getting a mind of his own.)

Same thing with Gaddafi, he too was not obedient enough, he started projects like getting water to the desert and the Gold Dinar. And he also needed to go so they can send immigrants more easily through a destroyed Libya. And why not destabilize one more Arab country which could help them in the future destabilize Egypt as well.