I feel that the whole subject of dwindling numbers is subjective and subject to location. If you take my location Dubai for instance we dont see this; let me explain further;
Im a member of a club, we have 110 diving members, and these members dive anywhere from weekly, monthly or occasionally. Each year we get 10 or so new members. These are generally OW (or equivalent) and we get them to AoW (or equivalent) the new members replace those we lose from people leaving the UAE (it being a transient place).
However there are many more divers than this here. Go to the LDS and each weekend you will see loads of cylinders being filled (Our club has its own compressor so we dont have to go to the LDS) All these other people dive. Equally on a weekend you can see 2 or 3 commercial vessels out with 20 or so divers on each.
Now the UAE isnt a diving destination, the West Coast has wrecks, which are all deeper than OW the Vis isnt great nor is the marine life. The East coast which is generally reached by day boats is better but still muck diving and macro (at Recreational depths) You have to go further afield and to be fair have some experience to Dive the Mussandam which is world class with Whale sharks and big life as well as nice reefs but unpredictable with currents as well as being true blue water.
My point here is that Dubai isnt a diving tourist spot yet we seem to have a very active diving community. You could say people here have a good disposable income and free time at weekends, however this place offers lots to fill your free time within 30 mins travel. So I would say if you took this location as a litmus test then diving is booming!
Lots of people tick off the diving done that box by getting their OW on vacation normally in clear safe warm waters with lots of life. Some keep diving every year on vacation some having got the cert go try other things?
Going back to the program how do you reflect diving? Like others have said watching divers for 10mins is about the max duration. Both National Geographic and the BBC both do fantastic nature programmes with lots of superb footage isnt that enough?
Furthermore you need to manage peoples expectations. Its okay showing how great the Red Sea or Caribbean is for instance, but if they then turn up at the LDS and do their OW in a murky quarry seeing a rusty bus in low vis will that keep the majority diving? I presume the vast majority who learn to dive locally get their cert to dive on vacation it is only the real diehards who are happy to dive anywhere?
And Diving isnt just about diving it can be social so having places where a group regularly hang out if theyre not diving also keeps retention. Certainly that Model works in the UK, it also works here where although we can dive all year round people choose to do social things often with fellow divers away from the water.
So in summary, and to counter opinion I dont see that diving is diminishing, I also see a range of ages diving both in our club and around the local community which probably emphasises the point that the popularity of diving is primary down to location, location, location?