I started a thread a couple days ago about how most liveaboards I've been on in my 20s have been full of older (50+ people) and if there were any that were younger. Someone pointed out it is a hallmark of the entire sport, and it got me thinking. I started diving in Hawaii when I was bored at a resort with my friends and decided to get a groupon for a diving certification. I liked it enough to buy a prescription mask that I still own. Since then I've been on 4+ liveaboards and multiple dives throughout Sipadan, Great Barrier Reef, Malapascua, Tulum, Turks and Caicos and now Maldives. The last two have been with Explorer, which while a great company I will never dive with again if I dive again. This is why:
1) culture clash of existing divers - Any young people who start diving are overwhelmed with all the old and not entirely welcome diver community. There is a real clash of cultures. The only millennials who have money to dive are probably like me - young, liberal, work in hot industries (tech, finance). Apparently having started out in the Navy and for some reason I don't understand profilgated in the Midwest and more Republican states most old divers I've met are from Utah, Idaho, Wyoming, Florida. Retired people in their 50-70s who cling to old ideas, are quite racist and sexist by my perspective (seriously this one dude Michael Ramsey on this boat called me a cockroach for being too aggressive - a quality that is prized in my current city of San Francisco - and something I'm convinced is due to racism/sexism - I'm an Asian female). They were in the military, run telemarketing firms (blergh), bankers, etc. nobody id ever meet or really gel with in real life. I've tried and I enjoy diving and I've met a couple amazing divers on my trips but there is something with the retired crowd that really reminds me of Trump supporters. And I bet a lot of them did. Also there is ageism in the tech industry so really I rarely meet anyone over the age of 45, and is argue techies are more likely to enjoy this sort of sport than finance types who want high luxury no effort.
I moved here to VA from SF.
Your post doesn't surprise me at all. You live in a pretty insulated bubble that has its own microcosm of cultures that are mostly pretty far removed from the rest of the country, much less the world. You have stereotypes that you apply to the people around you and, from your post, it appears that you live up to many stereotypes of San Franciscans.
I'm not saying your post is good or bad. Just recognizing where you are from.
All in all, I would say that if you want to keep diving, you should forget about liveaboards and book yourself to go places that offer the variety of activities that you want, including day charters for diving. Cozumel and Waikiki both come to mind. You can be around younger adults and have non-diving activities. I think you are also more likely to have some younger adults on day charters than on liveaboards. As you say, "your" crowd wants experiences without a huge investment. Going on a liveaboard is a big time and financial commitment. I would not expect people who are less "invested" in scuba to go on a liveaboard. I suspect that you yourself would not have been going on liveaboards except that, based on living in the Bay area, I would guess that you make more money than the national average for your age group. So, a liveaboard seems affordable to you where it's not to most people your age.
Asking the liveaboards to change to a format of offering diving mixed with other activities sounds like a tough financial proposition. You are (unsurprisingly) like the 2008 Obama supporters. Everybody wants change. Nobody agrees on what the changes should actually be. You all want a boat that offers more than just scuba diving, but what are the chances that everyone is going to be happy with 2 days of diving, 2 days of parasailing, and 2 days of jungle hiking? Just as an example. The notion that a boat could offer up a big ole smorgasbord of activities is simply naive. The cost for a berth on a liveaboard like that would be WAY more expensive than what they already are. The boat's costs to just offer one activity (scuba) well are high enough.
If you REALLY want to spend a week on a boat, and have a buffet of activities, then I would say your best bet is to find a charter sailboat, and charter it with a small group of friends. You can dictate what you do. Having the boat accommodate a few dives among other activities seems pretty feasible. Maybe even just put in at ports where you can rent the necessary gear and/or go out on a day boat from there, then back to your chartered sailboat after diving.