Thing is, as James Cameron pointed out in his interviews, this is not a cutting-edge field. The science of submersibles is well explored and the technologies are mature. Engineers know exactly how to construct a safe submersible to go as deep as you want. There are companies like this that make and sell these submersibles.

This guy was not doing research or experimentation. He was trying to cut costs because he probably couldn't afford a proper submersible under his business model and still make a profit. The only reason for using unconventional materials - materials that are well known to be unsuitable for this purpose - was that he thought he could do it more cheaply if he didn't go through safety certification or buy a sub that had already been certified. The point was to spend less money by taking more risks and make a profit. He was not innovating, and he was arrogantly overconfident, to the point of overriding all the experts who had warned him this would get people killed.