There was a ninja change in 5.1 to remove the 0/6 Display on the raid status .. now, when you have only to kill the last boss, you have no way to see which raid to join and so you end up in a lot of new raids. Which a lot of people quit on sight since that is not what they want.
But if you go that way you get a undeserved Deserter-Debuff ...
So right now, instead of quiting the raid, more and more people just strip their cloths and go afk, waiting till their boss arrives.
I was yesterday in LFR and got a DC on the Sha of Anger. I tried 8 times to just kill that boss just to end up in a new raid each time. The last time, just now, we had 10 nude people sitting in the entrance, waiting to be kicked so they can enqueue again .. but each time you kicked one you got a new nude one .. in the end the raid disbanded ...
EDIT: It seems that a lot people answer without reading what i wrote. At least in my case it's not about just wanting to kill the last boss only. It was about doing the raid 1h getting a DC on the last Boss .. and Blizz tries to force me to spend another hour just "for the fun of it" .. and I don't like that ... especially since that was a underhanded ninja change that doesn't solve any problem ...
And yes, you will see it my way once that happen to you too ...