Do you both mind elaborating more, for both my own curiosity, and perhaps a research note I can add in my final report?
For sure there are several ways to practice diving (and some divers practice several). An important one in France which doesn't seem to exist in the US (at least when coming from an online perspective) is through associative clubs. There is a strong network of non-profit dive clubs providing training with volunteer instructors, organizing local dives in lake, quarries, ... organizing week-end dive trips to the coasts, longer foreign dive trips. When close to the coast, those clubs often have their own boat(s). For some, most of the diving is through the club, with other club members as buddies. In that context, dive shops are diving equipment sellers and simply do not provide many other services, fills for clubs which don't have their compressor (many do) and when using the club compressor is not convenient, middle man for hydro.
At places where diving can be a viable industry (for instance on the Mediterranean coast) there are also commercial operators which have boats and professional instructors on staff and provide both training and boat dives. They often have a small shop, but selling gear seems more a service to their customers than an sizable source of income. Something they do is providing logistic (boat, fills, gear renting) for clubs, either local clubs like mine without a boat or non local clubs coming for a multi-day dive trip.
I'm living on the Mediterranean coast. I do most of my local (i.e. day trip) diving either with my club or commercial operators (where I go either alone -- they pair me with a buddy -- or with friends; there is a regulatory difference between coming with friends on a commercial operator dive and coming to the same operator with the same group of people as a club); from time to time a do a shore dive or a boat dive from a friend boat (and then a big part of the regulations just don't apply). I currently do all of my non local diving on trips organized by my club (with my children now starting not going on vacation with their father, I can see a change in the future).