Typically ships need to be certified by a classification society (an organization that inspects ships and makes sure they meet technical safety standards) in order to operate commercially. The Oceangate sub was not certified by any of these authorities because certification was viewed as “red tape” in the way of their “innovations”, and they would have almost certainly failed to be certified (a bad look if you are trying to convince people it is safe).

I think the rules/laws around commercial deep sea sub companies were unclear because most deep sea subs are research vessels or private projects (e.g. James Cameron’s sub), not tourist operations.