Most tech meetups don't fail because nobody shows up to the first event. They fail because nobody shows up to the fifth one. The gap between a one-off event and a community that sticks around comes down to a handful of habits organisers repeat without thinking about them.
The groups that last treat consistency as the product. A regular date, a predictable format, and a venue people can find twice without asking for directions again all do more for retention than any single flashy speaker. Members plan around routines, and a routine only forms if the routine actually happens.
The second habit is making it easy to come back with nothing prepared. Not every attendee wants to network, present, or even talk. Groups that keep a low-pressure "just come and listen" option alongside the more active parts of the evening tend to keep a wider base of regulars.
Finally, the organisers who build lasting communities close the loop after the event, not just before it. A short recap, a thank you, a link to slides, a nudge about the next date. It is a small thing, but it is the difference between an event that happened and a community members feel part of.