Death is known to be the most natural thing to happen. Yet, why do muslims suffer when someone they love dies? I, myself wish soon and beneficial death to the person I love, so he won’t have to face sins anymore. But then, as far as I know, our Prophet cried when his uncle Hz. Hamza (radiallahu anh) died. Why would our Prophet (sallallahu aleyhivesellem) cry , if he already knew that his uncle was granted a place in the Paradise?
That is because Islam does not replace our humanity. When we lose someone we lose a source of love and comfort, and that hurts. It is true that spiritually we can tell ourselves that they are now in a better place. But that does not change the material facts. We rarely feel so spiritual that the worldly life stops affecting us.
So intellectually one can say that the death of a loved person is not a tragedy. But since Islam does not replace our humanity, we still feel what any human feels, but our spirituality prevents us from going to excess in our grief.
Also, a person is not necessarily better off spiritually if they die sooner rather than later. The remaining years of their lifetime can offer them many opportunities to raise their spiritual status much higher than it is now. Since what we do in this world decides the qualify of our life in the afterlife forever, a person could wish to have as much time as possible to do good deeds and ask for forgiveness. It is therefore best to leave it to God to decide the best time for someone to die. We can never say with certainty that a person will be better off if they die now rather than later. Maybe God has great plans for them to help them attain His forgiveness and rewards.