There are currently two questions using cancellation, and one of them is barely relevant WRT this tag (which has now been fixed).
I'm wondering whether there's even a point to the tag in general: I doubt anyone is going to subscribe to it, since each cancellation of a TV show has its own reasons and anyone with knowledge about a particular case is most likely following the tag related to that TV show. Even more so when it comes to "cancelled movies".
Is "cancellation" really a topic that deserves a tag of its own? Sure, there are nearly 70 results that come up when you search for "cancelled" and 15 when searching for "cancellation". But I don't really see these questions as related to each other.
I feel this tag doesn't really add anything relevant, just like pilot or premiere or finale would. (Oh wait, pilot actually exists and has got two questions?)