Why was it canceled?

yeah, blame that on NBC ramming it down our throat by airing it 3 or more times a week.

The actual reason behind Deal Or No Deal's cancellation in 2009 was because of low ratings and trying to compete with other shows such as Dancing With The Stars. But I think the Million Dollar Mission caused the show's death because after trying multiple times to get a million dollar champion Deal Or No Deal finally scored two million dollar champions with Jessica Robinson and Tomorrow Rodriguez Deal Or No Deal lost it's luster and with the syndicated version now getting attention NBC decided to let the show run it's course. Soon after a week after it's cancellation GSN announced they were showing the reruns of Deal Or No Deal. But the CNBC revival of the show is really cool