I guess most of them now have families, all but killing new memory making opportunities? You also get older and wiser so no longer have catastrophic failures doing things (one of my group's* best memories was one guy taking mains electric while sat on his bent leg, flinging him to the other end of the bed where another dodged and saved his laptop - adults just don't do this) so life in general is more boring (from my singleton perspective, kids are supposedly a game changer) I've never been one to meet up just because though - if I see people it's to do something. As such we would be reminiscing over a pool table or game of poker so I have not noticed and been annoyed by the declining memory or repetitious nature of said reminiscing though it may well be happening.
Maybe when the kids grow up you'll be able to move on and make more memories when you have more spare cash, though it seems for most this time is spent/wasted with their partner.
*if you can call it that - there have been multiple 5 years gaps where we barely spoke and although we were meeting up weekly pre-covid I have only spoken to one of them once since)
Yeah, all of but one is married, and three of them have kids. The primary offender has five kids and lives a couple hours away, so, yeah, doing much with him besides the occasional sit and chat is out of the question.
I guess your point about adult life's boring nature and responsibility are probably the reason; whenever the conversation does divert from old memories, it's usually about home improvement, gardens, woodwork, work, or other such boring things.
Something else I've noticed about adulthood that may contribute is that even interesting things that happen nowadays don't really stick out or get retained in memory (unless there's a picture or video of it). Maybe it's because interesting/funny things in adulthood aren't all that novel compared to the rest of life up to that point.