Most deep sea submersibles only seat a couple people, which wouldn't work for the 'titanic tourism carnival ride' business model. I would guess the weight savings were intended to enable a sub with more capacity that could still be winched on and off the support ship without more complex/expensive heavy lifting equipment.
That was more marketing; the main biz model was to create enough buzz with the oil/gas industry to get bootstrapped and produce a product fleet of cheap subs for independent contractors to use for oil rigs.
https://www.fastcompany.com/40406673/the-man-who-wants-to-se...
The operators with the kind of risk tolerance to support this kind of, uh, venture can’t afford to do deepwater exploration - that’s solely the domain of the industry mega-giants, which are the most safety conscious and risk averse of all. The odds of getting a contract with, say, Exxon for anything resembling that piece of shit submarine are just vanishingly small. I actually don’t think the accident makes that prospect any less likely - it was already about as close to 0 as you can get.
A modern DSV for Challenger Deep (2x the pressure) used Isofloat to save weight and improve buoyancy.