The reason TV networks tend to air shows out of order (or at least in a different order than they were produced) is that they like to air what they consider to be the stronger or more audience friendly episodes first, so that way they'll attract a larger audience, who will hopefully stick around during the weaker or less audience friendly episodes based on the strength of the first few episodes. Which makes it frustrating if your show has a story arc each season and the network inattentively airs an episode with a huge revelation too early. Anyway, that's what they did with Star Trek, which is why The Man Trap aired first even though Where No Man Has Gone Before was the pilot.