Is another factor simply that, if you're the kind of person that's good at teaching people and you'd enjoy teaching people about Dungeoneering and how to do it effectively, there simply isn't any reward in-game for doing so and no way for other people in the clan to reimburse you for your efforts? You could easily empathise with someone who might want to train a new "meta" generation, but doesn't want to because they'd rather be doing the floors themselves with the fellow clan members they've known for months, years on end.
If team DGing is an example of emergent gameplay, then it stands to reason that Jagex won't necessarily reward everyone involved. But even on an interpersonal level, if you're a patient and understanding person who cares about the future of the skill, no-one's going to thank you for it except the ones you're training, and it's not going to get you that next chaotic any time soon.
Well, you're mentioning enjoyment. They could get enough enjoyment out of the activity and the structures that go with it and allow it to thrive (typically goes hand-in-hand with leading a clan about that). The teaching becomes secondary to the main activity of simply dg'ing. Most of the teachers in clans for aren't actual teachers -- they're experts in the area, and they share their knowledge, but they don't always know how to effectively convey it. Hell that's where a lot of the animosity towards DGS exists. They're amazing experts but teaching well to everyone, rather than just those with similar personality types to them, is not their strong point. (Not saying it it has to be, just making an observation.)
That said about enjoyment, I'm having a hard time understanding what you mean when you say Jagex doesn't need to reward people. I guess you could say the "reward" for getting better at DG was astronomically increased xp/hr rates. However, if they're removing the magnitude of that reward, doesn't that just reinforce the fact that people would eventually stop feeding into that cycle of growth for DG? It seems like we're both agreeing that it's collectively lowering the bar over time and killing it.