I'd also imagine that the tourists trusted the reputation of the operator. Both the state of the equipment and that their safety checks and processes were stringent. Especially since they claimed to aid in the science.
There aren't many priors for civilian submarine disasters.
Those things work right up to the moment that they do not, this stuff is at the cutting edge of technology and tourists simply have absolutely no place there. The only reason those rich folks tend to do stuff like this is because they like to brag about such stuff, not because they're interested in the science behind it (if they were they likely wouldn't go). The Titanic is less accessible than space.
Across history, for every 4 people who have summitted K2, 1 person has died trying.
Seriously: this is off the charts dangerous, the reputation of the operator is as good as their last dive.
It’s quite possible that they considered it and felt that it would compromise the structural integrity and the risk would be higher than not having it.