I would have thought this should be translated by a standard English passive: "Why is this disconnected?"
No, that would be מנתק. Sorry... I made it more confusing. :-)
ניתק / לנתק / מנתק משהו - disconnect something
disconnected (adj) - מנותק
get disconnected or become disconnected - התנתק / להתנתק / מתנתק
No, thank you, that made it much clearer. Thinking of the adjective first really does help.
But then the answer should be.. why does this become disconnected. Why does this disconnect.. Is an active phrase, surely. It suggests a fail safe, a trip switch etc. Hitpael is reflexive which is not reflected in their answer.