I believe it is because we were legally at war with Iraq. We signed a cease fire and not a peace treaty after Iraq invaded Kuwait. At the time there were 13, 14 Resolution passed by the UN. Remember, Resolution means final.
We upheld International Law and removed a threat. Hussein could have complied, but he wanted to be the big man who defied International Law. By upholding International Law, Khadaffy got the message and gave us the WMDs we knew he had. He received a message too.
I think this too:
Saudi is a problem, but if you remove the head, the people will try to put a wahabist in charge. These are not nice people. I am sorry to say, but I believe Ghengis Khan or an ICBM would be best suited for them. I almost think that osama put a lot of Saudis on the plane in hopes that we would have done to Saudi what we did to Afghanistan. So, we did it to the place that harbored him and had more people who were willing to work against the types like the taliban and al qeada. This is going to be a long war. We need to show these people that a hope and a future is with the Coalition and death is the life of a terrorist.