Something I've mentioned before, and others have similarly brought up, is that the "class" concept doesn't really fit many people's view of a fun way to spend time. Of course to many it does, but as I've said to my SO Lisamarie, "skiing is not a group exercise activity". To me it's an individual activity, with challenges and rewards that are primarily individual, though it may be done with others in the same time and place.
Just like there are people at the gym who do not want to take *any* kind of group exercise class, there are people who don't want to be instructed jointly. Or even feel like they are being "instructed" at all - they just want to "do my thing". They may want to "do their thing" with a buddy or spouse or a bunch of co-workers on a trip, but they don't want to "go to class".
Now for some, privates would be the way to go, but many people consider that only "experts" in a field want/can afford/are entitled to private lessons, a personal trainer, or whatever each particular sport's term is. Yeah that's not really the case, but I believe it is a common perception, even if somewhat an unconscious one.
I think the key for making group ski lessons more widely used, is not to make them "lessons" at all. I've personally found that the only type of "lesson" program I like is the multi-day "guided ski adventure" type of program such as Whistler's "Ski Esprit", where for 3 or 4 days you ski with the same instructor, and small group of people. And she (or he) takes you all over the mountain, based on your ability and potential, including dragging your butt out onto terrain that you *almost* could do but don't *believe* you can do - and then at that point, teaches you how you really can do it.
By presenting the reward (the tasty, challenging terrain you didn't think you could do) at the same time as the teaching for the last bit of skills you need for it, the instruction is eagerly absorbed, albeit sometimes with a bit of "you sure I can do this?" trepidation.
Meanwhile all of this is within the context of a lot of fun skiing all over the hill, with bits and pieces of instruction including various drills. But you're never just standing around for long in "class" - you're spending all day skiing.
I know for me, it was the only real way I felt that worked for me getting over the "intermediate hump" or at least getting a bit past that high intermediate threshold to "low advanced" on a good day, able to ski most fairly smooth steeps, or not-too-steep bumps.
That's not much yet by the typical Epicski standards, but it was a big leap for me. I never would have considered going out onto bumps deliberately - I was scared stiff of them from doing yahd sales all over a bump run years ago I got onto by accident. And never in a million years would I have signed up for an "intermediate bump skiing" class even though I've seen them offered. But in the context of a "guided skiing learning adventure" program I got at least a taste of why they are fun, and I also got enough skills to begin to enjoy ungroomed trails and bowls in general. Because I got real skill and confidence improvement from it, it's a definite part of any multiday trip to Whistler for me from then on. Because learning is *part of the fun* there, I don't consider it time taken away from the ski vacation.
At Whistler, they get huge numbers of people signing up for this, at all levels up through 9+, and it seems to be the primary way they market their ski school. They do have traditional group lessons, but they are downplayed. And they do have privates, but they are either half or full day, and priced prohibitively high for the average skiier. Perhaps Whistler's approach to privates is closer to what I said that many people perceive privates to be - something special for the higher end skiier.
I don't know if this concept works as well for smaller resorts, or weekend and day packages rather than multi-day, but I think it could be adapted. I know that in a day at Sunday River, I'm not really ever tempted to take out 2 hours for a group lesson, but I might well be interested in a full day's guided ski learning group.