The fourth season played **once** on Cartoon Network last October. After seven weeks, CN pulled the plug because they didn't have any more ReBoot (which was actually CN's fault, cause they had stopped the production of the toys a little while earlier).
Actually... I was one of those people who went to Toys R Us before the toys came out and had them check on the status of the toys on their computer. At first they had a lot of toys listed. They gave me the item numbers and prices on them. Then, when I came back later and asked the same question, hoping to get an update on the situation, I found that a lot of the items had disappeared from the listings. This was months in advance of the "Daemon Rising" showing, and makes me think that it was decided not to give it a decent airing on Cartoon Network well beforehand.