Even more discouraging is the extremely backwards way of thinking that the old farts in GA have. There is nothing that the barnacles who cling to the walls of the FBO hate more than change, and they're the ones buying stuff.
Most of that equipment selection problem can be traced back to poor quality instruction and conflicts of interest in the industry. Unlike flying, there is no legal licensing process for diving. Training is mostly handled by a few different private agencies which set course curricula and certify instructors. Some agencies have minimal quality standards and will give an instructor card to almost anyone. And then most training courses are run by dive shops which also sell equipment, so instructors are pressured to not criticize anything the shop sells even when it's total garbage.
The 'certification cost' is just the threshold at which the FAA is fine with all the liability being offloaded on to them, for engines made and maintained to spec at least.
i.e. For this cost to actually decrease would require an entirely different society, one that doesn't settle things through the judicial/administrative system whatsoever. But then costs may increase somewhere else.