I'm still catching up and trying to offer my own perspective. I joined the NE Ohio group of HSTA folks about 15 years ago and started doing day rides with them all over Ohio. Then I started going to rallies, I was still a relative newb to riding and was glad to be welcomed and get some advice and guidance from others. Flash forward 5+ years and some of our older members ride less, or are simply not around. Those who used to plan and lead rides are looking for help so I stepped in. I really enjoyed it and wondered (still do) why these much more experienced guys want me to lead them. Maybe its my map/road knowledge or my less hectic pace that keeps us in check (its a public road after all not a racetrack). It certainly isn't my riding skills, though I am getting better.
Flash forward another 5 years or so and it now seems like there is no weekend riding unless I plan something. When we go to an event if people want to group ride they find me and ask "where you going tomorrow." I don't mind the leading, and actually enjoy certain parts of it. But it just seems that too few people (even ones who've been riding for 30-40 years) have an interest in leading. I've asked about that before and don't get much in the way of an answer. Maybe they think I'm a control freak and now that I'm leading don't want to give it up. (They should have never given me this power.)
When I attend a rally I've always gone with at least one other local member. We ride together, if there are 4-6 or more we all ride together, with more we'll usually have multiple groups, sometimes doing the same ride. If there are only 2-3-4 of us occassionally (less than 5%) we'll join some other group and ride with them. We've also occassionally welcomed some other rider to join us. But for the vast majority of the time we are our group, and we ride that way. We don't really have any set rules, we just know what works. Sometimes we have a larger group, and linger at stops and BS more. We don't see each other often so that's fine, and we're not trying to get back by 3PM either (of course we left at 8-9 not 5-6).
Yes I know that doesn't help to get others to come along and join us, but it is what we do and what I suspect most members do. You may ride with people from other areas, but generally its your primary riding group at events.
I'm not sure how we change that or that you can change that. You aren't suddenly going to find others willing to lead rides for strangers if they don't lead rides with their friends or local riders. And those already leading are not going to want to add to their group, or leave their group to ride with others.
I think part of the problem (may have said this before) is people think that they come to an event and there is organized group riding, there isn't really. And I'm not sure how well it would work or if it is something that we really should be pushing for. I think the answer lies more in the local groups, but understand some members don't have a local group, they're the 2 new members from Rhode Island and nobody else is there (example).
Both Jims made good points about the generational gap, younger riders not having the time and money to travel. There's also a different attitude in wearing gear, being safe, not acting like a hooligan, etc. Most of that stuff won't sit well with an MSTA group, take off doing a wheelie from a stop and I'll pull over and ask you to leave. And Tosh is right about even cars, don't have kids but my 18 year old Nephew has no car and no desire to drive, have heard form co-workers with one or more kid that is the same.
One thing I've told my local riders, if we rode 15 years ago (when I was a newb) like we did today (faster, poor group riding etiquette, etc.) I'm not sure I would have stuck around. (I was mid 30s then, single had the money and a passion for riding, but scared silly about the potential dangers.)