The trick is consistency. Lock in a recurring time and place, so people can go mark a full year on the calendar. Nobody can make it to every one, but once people know others will definitely be there, it just grows on itself. People thrive on certainty. Totally different Steem experience when you have a monthly meetup to look forward to.
I compare it to skimming a stone. The stone is in the air most of the time, but just touching the water briefly every now and again, keeps its momentum going.