/who all LFG (level range) works in some zones, not in others.

[Ravager]

As the title says, /who all LFG (level range) works in some zones, not in others. Today I did /who all LFG 20 25 in Misty, Runnyeye and Gorge. It worked in Gorge and Misty, but not Runnyeye. And I know from experience it doesn't work in most zones. I'm just curious if anyone can guess why it might work in some zones and not others.