Just Finished Watching All of Firefly... WHY DID THEY CANCEL THIS SHOW?

Finished all 14 episiodes and this is an amazing show. I really want more of it. I know there is the movie Serenity which is to finish all of this. I have not seen it yet but I will do as soon as possible. This River girl is a total freak, isnt she? The last episode with her sneaky plan, that creeped the shit out of me. I really wanted to know more about River's secret and the facility she has been at. And who these feds with this weird device were. The romances should have been concluded with some serious love bullshit. Overall, a lot of unanswered questions. Also I really wanted to see a revolution or something taking place. There needs to be a sequel or spin-off. That would be so badass.