The 30+ crowd appears to believe that FaceBook is the most logical way to organize events - you can check in on your own schedule, without feeling pressured into immediately responding to someone poking you about joining up. Today's youth has no problem being expected to respond within minutes - or in the worst case, a couple of hours - to an inquiry made via SMS or Snapchat.
ie: Older person: "I may have some free time this weekend, maybe I'll check FaceBook tomorrow to see if anyone is planning something"; vs. younger generation: "Someone snapped our group telling us to come out with them Saturday, I'll decide in the next 5 minutes whether I'm in or out".