Problem is that comparing a submarine to a tank is completely invalid. These vehicles are just not the same.
If your tanks becomes unresponsive then you just get out and walk.
Try doing that 12,000ft under the ocean in a vehicle that is locked from the outside.
At that point, design and affordability should be at the bottom of the priority list. But, I guess when you're running a tourism business you gotta keep costs low so you can turn a profit #Capitalism ðŸ¤