The obvious first point is that this is a false analogy. Guitar students to not get certifications that tell music operators that they have the skill to do life-threatening activities.@BurhanMuntasser if your point is that people are getting injured or killed then let's talk about those specific incidents. I think it would be interesting and insightful to see what kinds of accidents are occurring when instructors with marginal training and no supervision are running classes.
If you're point is that it barks your shins because it's unfair competition, well, sorry, but I know a whole bunch of people with music degrees who complain about all the guitar teachers who don't.
But let's accept it for now.
You seem to be arguing that there is no point to scuba certifications that have an agency's backing. It could be like when my cousin learned to dive in the early 1960s, when the salesman at the sporting goods store where he bought his gear gave him a 5-minute talk about how to use it.
Are you arguing that trained instruction is unnecessary in modern scuba?