"NBC was considering paying for a second Pilot. We were having to recast most of the roles.
And then Desilu shut everything down. They were concern with how much they would have to spend.
They were already developing one show that was expensive, Mission Impossible. They did not think that they could afford to do a science fiction show. So Star Trek was shut down. It was not going to go to series,"
Interview with Gene Roddenberry, Starlog Magazine issue 30.