I think the reason group chats are gaining is because we are so numbed by all the public platforms. Between doom scrolling and ads noone pays any attention to personal posts anymore.

For me personally I would even go one step further and say that I'm really annoyed by people force-feeding me their peronal life/experiences.

Now they start (ab)using group chats for it:

A group created for organizing rock climbing activities: All of a sudden filled with photos of this summers vacation. OK, we are friends and know each other, but still...

Another one was for a specific training of a mountaineering club, people who just met for this one occasion: Half a year later someone starts posting photos of their latest trip. And then the next, ...

Maybe in my case it's the generation that started sm (lol) with attention seeking extrovert posts that do not get any attention on fb/x anymore, so they go to group chats.

What might still be true for younger people is that with all the noise on the internet a group chat may be a place that gives you a manageable chunk of content with a private touch that makes perosonal involvement worthwile/doable again.

And now let's watch it get abused&destroyed by corporations.