That's not the correct way to ask a (direct) question in English.
Indirect, yes (e.g. "I know why you don't rest." = I know the reason why you do not rest.).
But not direct ("What is the reason why you don't rest?") -- that has to be "Why don't you rest?"
May I suggest "why aren't you all resting?" as an accepted answer? I realize it's challenging to capture all of the colloquial ways to record 2nd person plural in English, and maybe the Southern US "y'all" is too regional, but i think it might help learners to have some options for translating ξεκουράζεστε as both formal and plural 2nd pers. Just a suggestion and thanks to all of you outstanding mods who read and help develop this program!