It's not that you've run too many — what we see again and again is that members learn: miss a one-off event and, oh well, there's always the next one. A giveaway is only ever “won / didn't win,” and once it's over they're left holding nothing.
Every recipe here hangs on the same thread: actions become points, points become rewards, and what builds up becomes levels — what members earn in this campaign is still there in the next. Missing out means earning less, and progress goes with them, so “dropping by to check” turns into a habit.
The 6 recipes above are campaigns with an end date; the 5 below are always-on programs where progress never resets to zero: campaigns bring the buzz, always-on programs keep people around.