Why do they keep doing this to us??

I don't understand why Producers & the whole group of people who are behind the scenes of shows do this kind of thing,it's like they sabotage their own shows, I really enjoyed this series, and then *Poof* it's gone... They seem to do this so many times to perfectly great shows with a decent plot and interesting characters, but they will run reality shows with the same premise season after season, but we get a taste of something original and they cancel it...