Gary Scott Thompson told TV Guide that high production costs had factored into the network's decision not to bring back the series following the conclusion of the writers' strike.
The final episode produced before the strike aired on February 15 and ended with a "to be continued" cliffhanger.
"[The episode] was actually supposed to be the first of a two-parter," said Thompson. "But that's as far as we got. We had three more episodes to shoot for the season, which we didn't get done."
Thompson is attempting to organise a direct-to-DVD ending but faces difficulty because the show is also produced by NBC. "It's all the same money," he added. "I've been making as many phone calls as I can make. I don't know who else to call."
The final season will air on Sky One in the UK later this year.