I don't think it is young people are too selfish or whatever (sorry, lot of people of us stalwart older generations were selfish too in our 20's, some never grew out of it...),that is just typical of old'uns complaining about the young, which a lot of it is we tend to forget when we get old what we were like when young. Culture changes over time,pure and simple. The KKK was once accepted and openly marched in parades,yet what they stood for became societally repugnant. Other groups that do a lot of good things in the world also became associated with political things that turned a lot of people off, it happens all the time.
I don't think groups like the Masons are going anywhere, any more than churches are or other things, but they likely will be much smaller going forward. The country is in some ways very much like model railroading (not surprisingly), there are a lot of cultures that make up the bigger one, and it changes over time, some things become bigger, others smaller. Some of the issue is that fraternal organizations can have bad perceptions around them, and that hurts them. The Masons, being a secretive organization, are ripe for conspiracy theories and all kinds of crap and many people associate secrecy with doing something wrong these days (and no, I don't share that theory, and while I suspect there is truth that the Masons have ties back to the old Knights Templar historically, the weird conspiracy theories around that are just that.
The other things as old things diminish or die new forms take shape. Sports fans of a particular team can be like that, with the advent of livestreams and the like there are whole communities around sports teams, that interact regularly and have their own thing going. Not saying virtual communities are necessarily the greatest thing or a replacement for real ones, but it for better and worse a new form of social community.
Then, of course, we have this forum, which is a kind of fraternal group, too (well, I never did figure out what a mixed social group is called, is it called fraternal, too, if co ed?).
I think if I build a model of one, I think I would put an Odd Fellows hall, the name kind of fits how I look at the world