The reason Meetup worked was years of collecting contact info of people interested in specific topics and then blasting all of them when a new group started in a location. If 1% of people responded, that was still a decent turnout.
This is the big barrier to entry for anyone trying to replicate Meetup. It was never about the event organizing software (which really wasn’t that great) it was about connecting your group or event to enough interested, local people that you had a chance at actually getting off the ground.
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.