okay, I'll bite
My premises: 1. Our troops were in S. Arabia to protect it and other countries from Hussein, and 2. Premise #1 was the only (somewhat) good reason for being there.
I can give a bad additional reason for staying - facilitating attacks on Syria and Iran, an extremely bad idea. A less-bad reason for staying is to make leaders in Syria and Iran worried about attacks, while never really planning to attack. It might work a little in Syria, won't work at all in Iran, and is far outweighed by the downside of promoting Islamic fundamentalism.