Because the accounting of all sins and the investigation and inquiry about them will destroy and ruin the sinner.

Umm al-Mu’minin Sayyidah Aisha (may Allah be pleased with her) narrates that I heard the Messenger of Allah (peace and blessings be upon him) asking for this supplication in his prayer, «‏‏‏‏اللَّهُمَّ حَاسِبْنِي حِسَابَاً يَسِيرَاً» ‏‏‏‏“O Allah, make my reckoning easy.”Then when the Messenger of Allah (peace and blessings be upon him) finished the prayer, I asked,“O Messenger of Allah (peace and blessings be upon him), what will an easy reckoning be?”The Messenger of Allah (peace and blessings be upon him) said:“The servant’s record of deeds will be looked at and he will be pardoned (for his sins). Because, O Aisha (may Allah be pleased with her), whoever is subjected to a detailed reckoning on that day will be destroyed. And whatever hardship befalls a believer, Allah, the Exalted, forgives his sins through it, even the thorn that pricks him (that too becomes an expiation for sins).”Both narrators have reported the words similarly.