Why would getting out of training kill the CDS? They have a very small number of instructors, and until they gave a free membership to new students, I bet the 1,000 members that the CDS has minus the lifetime memberships and minus the free memberships is a shockingly small number.
The argument that new diver training was what kept membership alive is what was used to keep the training side in the past, but I bet if you pulled all of their tax dox like we did when the NACD was dying, you'd see a steady decrease in the number of active members over the last 10 years.
You've basically made by point to be outside of instructors they have few members. So if you kill the training program, one where that requires the instructors to be members, and the students (through their instructors) pay cert fees you remove a lot of their non-donation income. All they would have left is their conferences, something that wasn't held for the last two years thanks to the CCP.
Alienating is admittedly a poor word choice for it, but your point that many of them don't even know it exists is part of the problem. If the instructors don't see a need to be a member of the CDS, then why would they tell their students about it? Instead, many of them talk about the NFSA and the awesome things they do, particularly at Peacock and Madison. If instead they were able to say "hey, you should give $15 to the NFSA because they support the state park sites, and you should also give $15 to the CDS because it holds these two awesome conference every year, they make sure that the caves have good lines and markers in them, good steps/benches at the surface, and whatever else they do, then I think you would actually get all of the instructors to push their students to join.
The old guys that actually talk history and who does all that work are a dying breed. Most students only hear about the NFSA after they do a repair project, and most don't know that all the gold line was paid for by the CDS. That is a marketing problem, send a videographer down whenever they are doing projects. Start marketing heavily, publishing blogs. Basically do everything that they aren't doing right now.
If the CDS instructor is primarily issuing certs for another agency, it is proof that they don't believe in the CDS...
In some cases it is like Jim points out, it takes a while for Adam to process the card. The other part is since students are paying for the card, most have never heard of the CDS but they have heard about the TDI. I personally get a TDI card in addition to my CDS card, for the reason Jim points out.