My partner and a friend both ran pretty big meetups 10 years ago. What made it good was the discoverability. As organizers they had to pay for the group ($80) but group members got free usage. Organizers and some groups charged to recoup but not the norm. There were messgae board and stuff but basically just a reservation system.

Somewhere along the way wework bought them. It’s been spun off, but downhill since. A lot of group organizers passed the groups to others and some groups disappeared.

I’m still a member of a couple groups and meetup is really pushing members of groups to pay now (join meetup plus), and more adds to click through when you rsvp.