Exhausted

I went through this last year after we killed the Lich King and it's happened again now, where a lot of folks are just done with raiding and nobody logs in. It is so frustrating to deal with this kind of thing after working so hard, and it's not like I haven't set expectations - everyone knows I wanted to progress into heroics but this week has seen a steep, steep drop-off in attendance. 40 - 50% of the raid just didn't show up. And I'm left scratching my head.

Am I doing something wrong?