Possibly because they are premium members and have had their vacation mode triggered by an impending timeout? As far as a I know this is the only exception to the rule that requires you to have made moves in all of your games before going into vacation mode.
Going on vacation while having to move in a game
I've known vacation protection to kick in with as much as 8 hours left. It prevented me moving on my mobile.
That seems like it's an excessive amount of lead time. Having the ability to change your vacation status from Mobile Chess would be a very useful enhancement.
My opponent had 2 hours left to move, has no possible chance in the game, is 1 move away from mate.....and went on vacation??
With 1 month and 29 days left...in a tournament.
Surely this is wrong...(and yes, I'm sorry for calling you surely)
I have had similar expereinces with players going on vacation while losing on time and position in a tournament. This is not fair.
If it's my move in a game, I can't go on vacation. But why my opponents can?