I think what we've shed are more things like chairing a committee for the VFW, selling snacks at little league games, or being active in a lowers voice, looks over shoulder union. These are things that would traditionally take up the social slack left by not punching a clock every day, and we've eliminated them systematically to make room for more marketized activities. Today's retirees are "richer" than their parents were, so they can take cruises, travel, pursue expensive hobbies, etc. but they largely don't have a social context to make those things satisfying, and there are fewer grandkids to take care of than ever.
Most unions pay their elected officers and administrative staff. Members might volunteer for some activities but the roles that come with a significant time commitment are jobs like any other.
VFW membership has declined because even with continuous wars for decades, the end of conscription has meant a lot fewer veterans. And many VFW halls functioned more like dive bars than anything else: nothing wrong with that, but not particularly attractive to most younger veterans.
The VFW is just a stand-in for any community "lodge" type organization, all of which have been in decline for decades. Yes, this is somewhat about the "cool" factor -- young people largely don't want to be seen in a Moose Lodge, Elk Lodge, Lions Club, Masonic Temple, etc., and these organizations typically have backwards views on female membership, have racist histories (or presents), etc. -- but the fact remains that, instead of doing this community-oriented thing, people are doing other, market-oriented things. Instead of playing darts at the American Legion, they are paying to go to an escape room, or even just staying home and gaming or shopping on TikTok. Even country club membership is in decline, so this isn't only a working class phenomenon.
I'm not as sure what point you're making about union staff. Surely there has been paid union staff for decades -- no real change there AFAIK -- and being "active" in the union doesn't mean you are doing paid staff work (though part time positions for retirees aren't that uncommon). There's a lot of stuff going in on a truly active union local that is definitely not paid work: being on the committee that builds the 4th of July parade float, organizing the games for the summer member picnic, organizing a group to go work in union colors at a Habitat for Humanity build, putting together care packages for sick members and sending groups to visit with shut-in retirees. You're right that, sadly, few locals are this active anymore, but it was once common.
In what way have we "eliminated them systematically"? Maybe I haven't paid close enough attention, but it feels like those activities have (unfortunately) disappeared largely naturally.
Take this question a step further and ask _why_ those activities disappeared. What are those people who would previously have been doing that, now doing instead? Usually, the answer is working. For the unions, decades of policy have systematically eliminated them, but for the other points, it's more of a "between the lines" thing.
If you look at any society in history, those things disappearing is the opposite of natural.
While it's true that there are some positive factors causing it (e.g. housework has been made far easier through inventing/factorying/delivering/installing of appliances like vacuum cleaners, washing machines and dishwashers, and the world has just become easier and safer to be in for women through things such as reliable cars with power steering, mobile phone, and policemen who respond) there are a lot of negative factors that just push those time-rich, more society enriching-capable women into the world of work.
The main one being what I already mentioned: house prices force them to work to pay a bank back for paying a boomer a massive price for a house, to keep up with the other two-income house bids.