Please keep in mind that recreational diving is not a growth industry, and in fact has been in a sustained decline since the 2007 financial crisis. Dive shops and operators are closing all over the place, or laying off DMs and instructors.
THat is an incredible sweeping statement, while it maybe true in the continental US, teh same can't' be said for the rest of the world.
I'm a silent investor in a small shop, in an area that mainly relies on its residents and not tourists for clients. My friend brought out a failing shop he's' worked in for 3 years. Despite the local economy contracting, with less discretionary expenditure available, and being 1 of 6 shops within a 10 minute drive of each other, he's doing okay. In fact my investment ( money I could afford to lose and in my mind was a gift) is seeing a small return.
Another friend has a centre in a location which relies solely on tourism, and is highly competitive with dive shops sitting side by side. She has built a successful business not just on day diving and residential Pro courses, Their main income is because she saw a niche and offers cheap but good food, and has a bar. It's the gathering place of teh strip for "sundowners"
In both these cases the people started out as jobbing instructors and got to know the marketplace - that meant them investing their time in courses and building their teaching experience and understanding the marketplace.
The dive industry is no different from any other service industry, but being a diver doesn't mean you'll operate a successful dive Op, just like some who is good at cooking may not succeed with owning a small guest house.