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.