Thanks for these comments. I think at the heart of this is the problem that caves are individually managed and the focus for each one is on "access to" whereas the difficulty for returning youth groups is a general problem of "access for". If caving wants to get serious about rejuvenating its ranks while focusing starter trips on places such as Goatchurch, then some sort of Young Cavers Award, a bit like a proficiency badge in Scouts, that shows you have got a certain level of experience and opens up more possibilities might be a good thing.
It will also require a shift in the attitude to commercial operators, because unless clubs are willing to operate in essentially the same way as a commercial operator would, it's impossible for schools to sign off a caving trip. So access is going to be limited to kids whose parents are interested - though it sounds like even then it's rather inhospitable.
We have done Waterwheel in the past too which is a good one. Andy and I have talked about Eastwater so that's a likely one. Can probably put together a third trip in the Mendips from such places and then it will have to be Wales or a longer trip to Yorkshire by the sound of it.
A few responses to specific things. I don't think one can really criticise the young people for wanting to go to different caves rather than exploring the further reaches of the same one. If the caves are nearer to you or you are going under your own steam and it's inexpensive, then you can be relaxed about going to the same places and squeezing the interest out of them. But if you get to go once a year and your parents have to pay for you to go away for the weekend, it's understandable that you'd want to be in a new space from the start of the trip, rather than spending a large chunk of it in areas you've been before. The pleasure in caving is a mix of sporting challenge, aesthetic appreciation and the excitement of discovery, and if you have few opportunities for it, it's great if those can all come together.
In terms of commercial/not commercial, I think it's a very crude distinction anyway. As I said in my post, I run an outdoor ed company (it's not my main income, and I'd be much better off if I concentrated on other more lucrative work) but these trips are just for fun. There was one occasion when think the trip cost me more than the it did the participants. On average over the years I have enjoyed free caving and have covered my travel to the school. I don't put in to my own company for the time on the caving trips, it's just the "wrapper" of insurance and so on that allows the trip to happen.
But why should it make a difference? I used to be a Scout leader and a teacher volunteer running DofE l. The trips I do now, both caving and DofE, are exactly the same activities. Scouting and other voluntary outdoor organisations are great, as are in-house school DofE programmes. But there aren't enough volunteers to meet the demand (fewer and fewer schools do DofE in-house), so commercial providers allow lots of young people to access outdoor activities who would otherwise go without. Because commercial providers are able to spend a lot of time on the work, they building up their expertise and that often feeds back into enriching voluntary activities. Lots of my instructors are still Scout leaders or do other volunteering.
I won't deny that the sniffy attitude some people have to commercial operators in the outdoors gets up my nose. Nobody is in it to make a fortune, but a professional instructor like Andy is responsible for thousands of days of young people enjoying caving who would otherwise never get the chance, and that's a good thing which I don't think is tainted in the slightest by his making a living from it. There are people working for charities that provide outdoor education who have had a far smaller impact, and who are paid a higher salary without the uncertainties of running a business, so I think the commercial/non-commercial split is a nonsense. What matters is the quality of the experience and the combination of participant competence/experience and supervision that makes for good safety and conservation.