Speaking for myself here. Might not apply to others, whether or not they planned to attend.
The thing is, you didn't post the place where we would be meeting up at 21:00.
So instead of idling uselessly in a city, I decided to take Garrshammer, ride around and herbalize the Broken Isles bare, because Thelarwen needed a huge stack of flowers for her inscription studies. Had I received a ping "we are meeting in Stormwind/Tanaris/Shattrah/Borean, get yer arse there!" I'd of course have parked Garr, logged Thel and skedaddled over.
Then again, it seems that most people are still busy with leveling, questing and dungeonating. I think there's a certain ideal time range between "too busy with new content" and "too bored so I'm unsubscribing" where people would go "hey, let's join an event". But this might not just be right now.