All because they forgot Allah…

فنسيان ذكر الله مـــــوت قـــــلوبهم           وأجـسامهم قـبل الـقبور قبور .
وأرواحهم في وحشة من جسومهم           وليس لهم حتى النشور نشور 
The forgetfulness of the remembrance of Allah is the death of their hearts

Their bodies are graves before the eventual grave

Their souls are in solitude away from their bodies

And they will not be resurrected (their bodies or souls) until the Day of resurrection (i.e. Judgement day)