Here's what happened with Tru Calling.
It's ratings were never spectacular, BUT they were ALWAYS pretty even and the show never dropped significantly. Also, fans and critics were liking the direction the show took in the second half of the season, saying it was the most improved show of the year, etc. So FOX took the high road (at first) and basically ordered a second season because they wanted to prove to viewers they were willing to give their "cult" shows a chance and let Tru develop a larger audience. They ordered 13 episodes, with the idea being that they'd order more if ratings improved at all.
Then, during the summer, something obviously happened and FOX decided to bail on Tru even though they had no real reason too. Partly it was due to "Point Pleasant"...they seemed to only want ONE genre series on the schedule, and they felt that a NEW show had a better chance. In fact, PP has a LOT of the same crew as Tru did. So they ended production on Tru which was filming it's sixth episode.
When Point Pleasant failed (which was sad, as I love PP AND Tru) they decided they would air the six episodes. Ironically, the show had virtually NO promotion whatsoever yet premiered to the same number of viewers that it was averaging in season one...a little more that 4.5 million viewers. And then they pulled the sixth episode because it was April and the last one was a Christmas-themed episode. *sigh*
So despite what Tru haters may say, and what FOX believed in the beginning, this show's viewers were LOYAL...otherwise those five season two episodes would not have kept all its viewers from season one. And the show *was* getting better and better all the time.
And BTW, I'd like to add that it's not fair that people insult the fact that the show had no true arcs during the first half of the season. It was more along the lines of the writers doing viewers a favor. I mean, they had no reason to believe there was a real chance of being picked up for an entire season, so why introduce a villain for Tru early on? Why get into the really heavy arc stufff? That's why it's all introduced in episode 14, which is the first episode made after FOX's initial 13-episode pickup.