Probably because it is close to impossible to find a picture of the Corsair II with fully clean wings. I have come across pictures with 2 pylons removed, one on each wing, but not all at the same time. Here are a couple of pictures I consider to be popular with the middle pylons removed:
Note, that in the second picture, the innermost pylon is still there despite being empty. May be a drop tank was hanging there and was dropped before the picture was taken, who knows...
I would say that considering the lack of pictures of Corsairs II without pylons, TK decided to represent the aircraft with pylons on at all times.