I think it boils down to money, in the end. The outfit is officially licensed, and the image is clearly a stock photo. Some company got a license to make an outfit for Ghostbusters. The leads were all male, so they figured "Hey, most of the costumers will probably be male", and hence they chose a male in the picture, even though the costume looks more unisex than a standard issue toilet.
The new costume is more feminine and mostly directed at women. The picture is of a woman, which is natural, considering the female leads in the movie.
I get it, there's a lot of shit in this world with sexism, lack of rights for women and so on. But this, in my opinion, isn't an example of institutional sexism.