It's a bit of a generalisation, but commercial diving is hard work, and often in unpleasant environments.
The other obvious option, instructing, involves a lot of competition for a relatively small number of jobs - particularly if you are looking to travel to popular destinations such as the Red Sea or the Great Barrier Reef. If you go to Cairns, for example, you'll find most of the dive operators have signs in their windows saying "Instructors, please do not ask us for work".
The people who "make it", by which I mean get the life style they want and can afford to maintain, tend to have a lot of arrows in thie quiver.... so for example, a boat handling qualification and a service technician course as well as being an instructor or commercial diver.
The minimum you'll need to find work will be a DM (or DiveCon or equivilant) qualification, so that at least gives you a shorter term goal.