Horizontal cocks are in

the two types of Hecbear

they have to get surgery that rotates their cock and balls 90°

It's a diver's dry-suit. They're for peeing without removing the dry suit, they have full normal clothing on underneath so presumably the horizontal zip as the top layer makes it easier to access a wide range of clothing that could be underneath it.

I think also the zipper teeth on a dry-suit are much larger so they add a lot more bulk that's easier to put on the suit horizontally anyway. This thing seals completely water tight.