Bro!
event *we* want = event in which you (or others you included into *we*) have to unlock girl cards [I assume]
1. How to have Rankings and rewards if only few players are playing an event.
2. AND If you get to play an event without rewards , Then TOP/experienced/Large Player base certainly do not want to play such event.
Note that the number of girl cards you can get from defeating event monsters only is absolutely crap when compared to what you can get from Event Chest(s) and Total overall ranking.