The 1989 Deep Six is not a beloved figure. He is, though, a pretty great figure for his specialty. He was the perfect blend of 1989 modernity that defined the Joe line and old-timey diving suits that every kid in the '80's knew from the Fisher Price figure that came with the orange octopus. Originally, though, the figure was supposed to include even more gear than he did. Along with all his production pieces, Deep Six was also going to include two diving shoes that attached to his feet. You can see them in the catalog image below.
It's certain that these shoes were removed for cost cutting reasons. They really offered nothing to the figure. And, Deep Six included a nice amount of gear, even without them. And, no kid was making a purchase decision on Deep Six based on whether or not he included some weighted shoes. They were small pieces that would have been easily lost. So, much like Mainframe's computer stand from 1986, the accessories were entirely superfluous and didn't really affect the overall impression of the figure were they removed.
If you look very closely at Deep Six's card artwork, you can just barely see the shoes. Hasbro was deft in their editing, though. And, the bottom of Deep Six's feet are cut off by the edges of the card. Knowing the shoes were axed and this would have just been a matter of cropping the photo slightly differently, it's tough to see the feet being so close to the edge as anything other than intentional.
It's always interesting to see items like this. We know that the cost to develop an accessory is the biggest part of the overall expense. But, even in the late '80's, Hasbro was making at least 150,000-200,000 of their least popular figures. So, saving a few pennies on a figure could add up across the whole line...even if Hasbro had incurred the cost to make the parts. The shoes appearing in a promo catalog with production level figures, though, tells you they were a late strike from the figure's complement of gear. While I would love for their to be a complicated back story as to why these pieces were chosen for elimination, the truth is that it is certain to be nothing more than financial. And, decisions like that are both boring and depressing while also driving home that, to the Hasbro guys, the Joe line was, at the end of the day, a job.